There's a handful of numbers throughout baseball history that are so important, so revered, so iconic that they require no additional explanation. 714 and 755 count there, as do .406 or 56 in a row. If we're going past baseball card stats to uniform numbers, then 42 is part of that club too. You immediately know what all of those mean.

For nearly 50 years, 660 has been one of those numbers, too. Willie Mays hit the 660th and final regular-season home run of his career on Aug. 17, 1973, at Shea Stadium as a member of the Mets off Cincinnati's Don Gullett. Sure, he hit one in the playoffs ('71), and three more in All-Star Games ('56, '60, and '65), and assuredly countless more in Spring Training and other exhibitions, but 660 is the number. It's on his Hall of Fame plaque. It's on some of his autographs. It's written on the wall at Oracle Park. When someone passes 660, it's a big deal. It's as associated with Mays as the 24 he wore on his back.

That No. 24 is never going to change. But the 660, believe it or not, might. Forty-seven years after Mays last played professional baseball, he might have gained another dinger. How does 661 sound?

What we're about to explain is not set in stone, to be clear. There's a great deal of research, clarification, approval and updating to be done. But as that research continues, so does our understanding of the historical record.

“We do have that one home run … 1948 for Willie Mays," Larry Lester, prominent Negro Leagues historian, said on Thursday's episode of the Ballpark Dimensions podcast. "We’re going to add that; he’ll have 661. We have found that box score.”

So long, 660, hello 661? That would be earth-shattering. Let's explain how we got here.

On Dec. 16, Major League Baseball announced that the Negro Leagues -- specifically a group of seven leagues that were active between 1920-48 -- would be given Major League status. This was done to rectify the misguided decision of a "Special Committee on Baseball Records" that convened in '68 and gave four historic leagues (alongside the current American and National Leagues) Major League status, but failed to even consider the Negro Leagues. This designation was long overdue and beyond necessary to recognize that Black and Latino players from generations ago were not lesser and are not to be overlooked.

"It does give additional credence to how significant the Negro Leagues were, both on and off the field,” said Negro Leagues Baseball Museum president Bob Kendrick. “These men and women, from players to owners, didn’t need validation from anybody. For me, this move by baseball is more about righting a wrong,” he told legendary sportswriter Claire Smith.

That immediately opened up the baseball world to a ton of questions about how the inclusion of Negro League stats might change the numbers we all know. For example, Hall of Fame shortstop Joe Tinker's career stats include his time in the NL and his two years in the upstart Federal League of 1914-15, which is considered a Major League. He has 31 career homers, which is a combination of "29 in the National League and two in the Federal League." Conversely, the player pages of Major League legends like Mays, Jackie Robinson, and Larry Doby do not include Negro League numbers -- yet, anyway.

As we tried to speculate, using the Negro League database compiled at Seamheads.com, it seems like including these stats might have some significant effects on the all-time leaderboards. Josh Gibson won't be the all-time home run leader, but he might have the best single-season batting average (.466 in 1943). There are going to be about two dozen new no-hitters, including Leon Day joining Bob Feller as the only men to throw Opening Day no-nos. There are going to be many more changes like that to come.

But that work is not yet complete, as only about 75% of box scores for known Negro League games between 1920-48 have been collected and catalogued in the Seamheads database. Without a box score, there's not going to be an official number, even if an event was known to have happened. Like, say, an extra home run for Willie Mays. Mays played briefly for the '48 Birmingham Black Barons, and there are no home runs noted on his Seamheads page. But as Ben Lindbergh, who deserves a great deal of credit for bringing the issue of status for the Negro Leagues to the forefront this summer, pointed out this week:

"Mays went deep at least once in his rookie campaign for the Black Barons, but a box score hasn’t been found. Until one is located, his famous mark of 660 homers will stay the same."

And that, we figured, was that. That one Mays home run was likely in that missing 25% of box scores. It might take years for it to be found. It might never be found. Six hundred and sixty won't be going anywhere, any time soon.

Except ... on Thursday, we invited Lester to join us on the podcast to discuss the process of getting to this point, and how the news affected him. After all, Lester is co-founder of the Negro Leagues Baseball Museum and chairman of the Society for American Baseball Research's (SABR) Negro Leagues Committee. He's an accomplished author and editor in many fields, and he is one of the most prominent Negro Leagues researchers. It's likely none of this would have been possible without his efforts.

When we brought up the point of the missing box scores, he concurred but said there would be more to come.

“We’ve found more than that," said Lester, "but we only have about 75% in the database right now.”

So right away, we knew that our speculative guess at how numbers would change -- like Gibson's possible .466, or his 200 OPS+, or Satchel Paige's additional 1,563 innings -- was incomplete. Those numbers can and will change as more information is entered.

"We have found probably 99% of the games in the 1920s, and the '30s are hit and miss. In the 1940s and late 1930s, we've found probably 90% of the games that were scheduled," Lester continued. "We're in good shape. It takes a while to to crunch the numbers. Every line of that box score has to be manually inputted into a spreadsheet, which is uploaded to a database that I created.

"And that database information goes to Gary Ashwill with Seamheads, so that that data is available to everybody on the internet. We'll get there, and it will change some of the records, good bad and indifferent. Some people will be upset to find out that Josh Gibson never hit 800 home runs."

But the real news wasn't what hasn't been found yet. It's what has -- that one missing Mays home run.

That home run was hit on Aug. 11, 1948, when Mays would have been about three months past his 17th birthday. As Lindbergh noted, that home run was mentioned in newspaper stories. It came in Birmingham, and if this news story is accurate, it was hit off of 20-year-old Panamanian Vibert "Webbo" Clarke of the Cleveland Buckeyes. (Clarke would later go on to briefly appear in seven games for the '55 Washington Senators.)

So if the box score exists, and it just hasn't been entered into the system yet, it seems likely that soon enough, it will be. (As the process continues, MLB and the Elias Sports Bureau -- MLB’s official statistician -- are convening on an official review to determine how to proceed.) Mays will have 661 Major League home runs -- 660 NL homers and one in the Negro Leagues. One regular-season home run, anyway.

“We also have a home run that he hit in the third game of the World Series in 1948," Lester continued. "There was no box score. Albert Pujols is safe for right now with 662 … but don’t count me out yet. I’m still searching.”

Of course, Pujols also has 19 postseason home runs, and we're not counting those in his career total. Six hundred and sixty-one, if and when that's what Mays ends up with, would seem to be safe.

In 2015, the New York Times recounted Mays' final home run in a story that carried the headline "On the Night Willie Mays Hit No. 660, It Was Just Another Number," pointing out that it carried little fanfare because it broke no records and with six weeks left in the season, no one knew it would be his last; functionally, it was no different than No. 657 or No. 648. It will always be his final home run, but maybe the Times was more correct than they knew. Maybe it was just another number.