If general managers of baseball teams still used paper calendars and magic markers, they would have circled those calendars years ago, drooling with anticipation for this winter. Bryce Harper and Manny Machado are multi-tool superstars in their mid-20s, making them the kind of ultra-rare players who could smash the all-time record for biggest contracts in baseball history.

The bad news is that 28 (or maybe 29!) teams will lose out on the Harper and Machado sweepstakes, leaving a lot of disappointed shoppers ... or, let's be honest, a handful of disappointed shoppers, and an avalanche of teams that wouldn't spend $350 million-$400 million on one player if the world were about to end.

That got us wondering: What will be the next mega-class for free agents? Which market projects to generate bidding frenzies for multiple players, maybe even eclipsing a 2018-2019 class that, aside from the top two, looks like a dud?

You can find marquee potential free agents in each of the next five free-agent classes, to be sure. If you're the impatient type, dive right in next winter for Nolan Arenado, Paul Goldschmidt, Anthony Rendon, Chris Sale, Gerrit Cole and Xander Bogaerts. The Class of 2022 could be a banger, with Aaron Judge, Alex Bregman, Trea Turner, Andrew Benintendi, 2018 Cy Young winner Blake Snell and 2018 MVP winner Christian Yelich leading the charge. Even further out, Jose Ramirez and Cody Bellinger headline a Class of 2023 that could fill up with stars as some of the most promising youngsters in today's game enter their prime. It's tempting to give the title to the Class of 2020, since 2018 AL MVP Mookie Betts will hit the market just after his 28th birthday ... and even he will take a back seat to the best player on Earth, Mike Trout.

With due respect to all those classes, there's one winter that could bring both gigantic top-of-the-board deals and one of the widest array of stars in the nearly half-century since Andy Messersmith and Dave McNally ushered in the free-agent era.

It's the Class of 2021. The Year of the Shortstop.

The Class of 2021 features three Rookie of the Year winners, one MVP winner, and a slew of All-Star appearances, Gold Gloves, and Silver Slugger awards. But as the market for Harper and Machado will demonstrate (and as the market for other young free agents like Alex Rodriguez and Jason Heyward has taught us in the past), upside means everything in free agency.

Baseball's increasingly shrewd and risk-averse group of general managers don't want to pay for past results. They want to pay for future potential. That means finding free agents who exhibit the rare combination of proven results, excellent health, and the kind of youth that's tough to find, with most first-time free agents coming out in their late 20s, or even their early 30s.

The Class of 2021 offers an impressive list of players who check all those boxes. There's also a handful of stars who'll be seeking their second big contracts, yet figure to bring in big bucks due to their perennial big numbers (assuming that holds true for the next three seasons). The biggest marker for this free-agent class, though, is its embarrassing wealth of shortstop riches. This is the A-Rod/Jeter/Nomar class, only if all of them hit free agency at the same time, and Nomar didn't curse himself into oblivion.

Here are the shortstops who could earn more than the GDP of several Pacific island nations three years from now, along with the star-studded supporting cast who could make the Class of 2021 one to remember:

Francisco Lindor
NYM • SS • 12
Age on Opening Day 2022: 28
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Once upon a time, not that long ago, Lindor was revered as an all-world gloveman, but also derided as a popgun hitter, someone who made frequent contact with the ball, but rarely did anything exciting when he did connect.

Covering Cleveland's top 10 prospects for the 2014 season, then-Baseball Prospectus writer Jason Parks listed the following as Lindor's weaknesses:

"Hit tool might lack impact; could play below projection and play to (only) solid-average; contact can be soft and slappy; well below-average power; not a burner; doesn't play for your team."

That was Lindor in a nutshell. A marvelous fielder who ran well, but was coming off a season at Single- and Double-A in which he hit a combined two home runs. Even with that glaring weakness on his resume, Parks lauded Lindor's overall ability, labeling him Cleveland's top prospect and one of the best in the game. Lindor flashing Gold Glove defense and his mile-wide smile for a team that wasn't the one you rooted for would be cause for 29 fan bases to be bummed.

The terrific defense is still there five years later, as is Lindor's superior contact skills and infectious enthusiasm. Also there: the kind of booming power you'd normally associate with players 50 pounds heavier. Lindor has smashed 71 long balls over the past two seasons, the ninth-best mark in all of baseball and just one behind overlord Mike Trout. In just three full seasons, he's already finished second in Rookie of the Year voting, won a Gold Glove and two Silver Sluggers, made three All-Star teams, finished ninth or better in MVP voting three times, and flashed his full set of pearly whites before, during, and after all those improbable home runs.

Call it impressive development, a stark example of juiced baseballs juicing home-run totals, or a little of both. Whatever the case, Lindor is an incredible all-around player who's also supremely likeable, with improving numbers every year. He'll be a little older than Machado and Harper are now, but that's not going to stop him from becoming very, very, rich three years from now.

Carlos Correa
HOU • SS • 1
Age on Opening Day 2022: 27
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If Lindor looks like a shortstop -- 5-foot-11 in shoes, lithe, and quick-twitch -- Correa looks more like a free safety or a linebacker; check him out standing next to Houston Texans behemoth J.J. Watt, and tell me Correa looks like shortstops of 40 years ago. With size and strength like that, you'd expect Correa to already have some Nintendo-like stat lines under his belt.

Instead, injuries have held him back, with Correa topping 110 games played just once in his first three full seasons, with a relatively modest career-high of 24 home runs. His 2018 line of .239/.323/.405, with a strikeout nearly every four times up, doesn't exactly scream out future MVP winner.

The universal consensus is that last year's struggles stemmed from back and oblique injuries, and that Correa's blend of raw talent, brute strength, and untapped upside may well start to deliver some shiny hardware.

Corey Seager
LAD • SS • 5
Age on Opening Day 2022: 27
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As Heyward, Eric Hosmer, and others can attest, timing is everything. Peaking right before free agency can add tens of millions of dollars to a player's next contract.

Seager needs to work on his timing. In 2016 he delivered one of the best rookie seasons of all time, batting .308/.365/.512 with 71 extra-base hits, while playing at pitcher-friendly Dodger Stadium. He's gone backwards since then, hitting for less power and striking out more in his sophomore campaign, then missing most of 2018 following Tommy John surgery, plus an additional procedure to repair a torn hip labrum.

At his best, Seager is a master at hunting pitches he can clobber, then following through on said clobbering. He's just five months older than Correa, with a huge skill set for a player at a premium position like shortstop. He just needs to next three seasons to look a lot more like his first.

Trevor Story
COL • SS • 27
Age on Opening Day 2022: 29
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The longest-hit baseball of the 2018 season wasn't smoked by J.D. Martinez, Khris Davis, or notorious tape-measure maestro Giancarlo Stanton. It was a 505-foot moonshot, off the bat of Trevor Story ... who crushed a total of seven homers that traveled 459 feet or more last season. Story hammered 37 pitches into the bleachers in 2018, with most of his longest blasts coming at Coors Field.

Therein lies the focus of a future debate. Just as Rockies hitters get crushed when Hall of Fame voting season rolls around, Story could be an interesting test subject for the free-agent market -- two years after his even more explosive infield partner Nolan Arenado is slated to go up for bid. If Story continues his across-the-board improvement in plate discipline, hard contact, pull rate, and other underlying indicators, he might still cash in ... whether via free agency, or a Todd Helton/Charlie Blackmon-style re-up in Colorado.

Javier Baez
NYM • 2B • 23
Age on Opening Day 2022: 29
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We're cheating a little here, because Baez has played more games at second base than at short in his major league career. Still, he's logged 138 games at shortstop over the past two seasons, flashing slightly better-than-league average defense at that spot, thanks in part to his supernatural tagging skills that play well at both middle-infield spots.

In even more exciting news, Baez turned into a planet-devouring monster at the plate last season, pounding 34 homers and 83 extra-base hits, hitting .290, slugging a massive .554, and stealing 21 bases with plus baserunning results to boot. There are still holes in Baez's game, including an ultra-aggressive, ultra-violent swing that creates Gary Sheffield-ian damage when he connects, but also a strikeout-to-walk rate of nearly six-to-one last season.

Still, Baez checks all the boxes: potent hitter, solid fielder, durable, charisma dialed up to 11. If this is your team's consolation prize in the event it misses out on Lindor or Correa, you're doing pretty damn well.

If those five shortstops and a few lower-end guys comprised the entire Class of 2021, that would already be pretty attractive. But the free agents who'll hit the market three years from now also include a murderer's row of starting pitchers.

Max Scherzer and Corey Kluber already have five Cy Young awards between them, and could still be highly attractive commodities on their second long-term contracts, in their 30s. Noah Syndergaard and Aaron Nola also wield Cy Young-caliber stuff, with Nola breaking out with 212 ⅓ innings and a 2.37 ERA in 2018. The list of top hitters includes 2016 Kris Bryant (likely to rebound after a shoulder injury held him back last year), Cubs teammate Anthony Rizzo (who'll be 32 after the Cubs presumably pick up their 2020 and 2021 options on him, but still offers one of the best combinations of power and patience in the game), and Freddie Freeman (who just missed going .300/.400/.500 for a third straight season, and a player who broke into the majors at such a young age that he'll also be just 32 heading into his 13rd major league season). Michael Conforto, Starling Marte, Jon Gray, and other talented players round out what could be one of the deepest free-agent classes of all time.

Things will change between now and the fall of 2021, of course. Josh Donaldson's injuries and Clayton Kershaw re-signing with the Dodgers took some of the juice out of this year's Harper/Machado class, and we'll almost certainly see some injuries and contract extensions thin out future free-agent markets too.

Also, the talk of record-setting deals for Harper and Machado is still just talk. It's possible that even top-of-the-board players might feel the pinch that's come from more conservative GMs holding the line, and that the Class of 2021 could be further affected by a potential labor stoppage as the current collective bargaining agreement expires and players fight back against an increasingly shrinking piece of MLB's revenue pie.

But it's still fun to dream. And if you're a fan of a rebuilding squad of the dozen or so teams in the midst of rebuilding, The Class of 2021 may well deliver that elusive superstar, the one final piece of a World Series-winning puzzle.