McCann is also a little hazy on Clemens' first three Cy Young Awards -- since all of them came before McCann had made it out of the first grade.
And you can especially cut McCann a break if he can't quite recall the buzz that surrounded Clemens' big-league debut -- since McCann had been hanging around planet earth for exactly 85 days when it happened.
But the beauty of baseball's October plot lines is that they often bring together the unlikeliest of co-stars. And what happened Thursday, when Brian McCann faced the great Roger Clemens for the first time, was about as improbable as these insane October scripts ever get.
The scoreboard tells us that the Atlanta Braves won this game 7-1, evening their NL Division Series with the Houston Astros at a game apiece. But that score isn't what the 46,181 water-logged customers at Turner Field will always remember.
It's what happened in the third inning -- when a 21-year-old rookie catcher hit a home run that will be traveling for his entire lifetime off a 43-year-old living legend.
One second, we were all busy savoring one of the most storied postseason pitching matchups ever staged -- John Smoltz vs. Clemens, 518 wins and 7,069 strikeouts worth of brilliance centered on the same pitching mound.
And the next second, it was time to tear up our original screenplays and interrupt our regularly scheduled Cy Young programming.
Suddenly, this was McCann's show.
There were two men on and two men out in the third inning. The Rookie had run a 2-0 count on The Legend on the mound.
So the Rocket Man reached back to do what he had done 2 trillion times before in his astonishing career -- whoosh a first-strike fastball past a kid whose kneecaps were rattling at the mere thought of facing him.
But then an amazing thing happened. As Clemens' 93-mph scorcher headed toward home plate, it was met by the flash of McCann's bat. And there went the baseball, boring a hole in the drizzly October sky.
It didn't come down until it had turned into a souvenir for a lifetime. And a 1-0 Houston lead had disappeared in the vapor of a magical three-run homer.
"You never expect to hit a home run off a guy like that," McCann would say, three spine-tingling hours later. "He's the best pitcher in baseball. He's been the best pitcher in baseball -- him and Smoltz. He's a first-ballot Hall of Famer. So this is something I won't forget."
Then again, this is something the world won't soon forget, because even McCann himself can't comprehend just how miraculous and historic this home run was:
• Never in history, according to SABR home run historian David Vincent, had any previous player hit a postseason home run off a pitcher who made his big-league debut in the same year that the hitter was born.
• And never, according to the Elias Sports Bureau, has there been a bigger age difference in history between a home run hitter and the pitcher who served it up than the 21-year, 200-day gap between Clemens and McCann.
• Never, either, has a catcher younger than McCann (21 years, 6½ months) hit a home run off anybody in a postseason game. (Previous record-holder: Someone named Yogi Berra -- at 22 years, 4½ months.)
Amazing, amazing stuff. But that's not even all.
• McCann is the first Brave in history to hit a home run in his first postseason plate appearance -- which means that among the guys who never did were Hank Aaron, Eddie Mathews, Dale Murphy, Joe Torre and those two Joneses.
• He's the first catcher to do that since 1913 (when Wally Schang became the only other catcher ever to homer in his first postseason at-bat).
• And McCann is just the second Brave to homer off Clemens in any postseason game, joining only Andruw Jones (who did it last year).
Yes, it was a moment so cool and so special that even the guys in the other clubhouse understood exactly what it meant, even if it wasn't quite their favorite highlight of the night.
"You're never going to forget certain things that happen to you in this game," said Houston's Craig Biggio, a guy with 18 years of memories of his own. "And a three-run home run off the Rocket in his first playoff game -- I guarantee you he'll never forget that. It was good for him, just bad for us."
"That kid should save that bat," said Jeff Bagwell, a guy who has played 15 seasons -- but hit only one more postseason home run than McCann. "And one of these days, he should sneak in and have Roger sign it. ... Uh, today wouldn't be a good day -- but someday."
Even Clemens, wizened old-timer that he is now, admitted that there is a part of him -- buried inside that seldom-seen Kinder-Gentler compartment of his soul -- that comprehends how memorable a development this was for the guy on the other end of it.
As McCann's home run soared off into the night, Clemens turned his head to let the kid who hit it relish his euphoric trip around the bases -- and never turned back toward home plate until McCann had made it all the way back to the dugout.
"I was just sitting back and letting him enjoy it over there," Clemens said. "I mean, what else can you do? It was a very hittable pitch. Guys on this level, whether they're 21 or 41, are going to hit that. And he took advantage of it. I've given up some home runs, I'm sure, in my career. But it was probably pretty exciting for that kid."
Um, probably? Asked to recall how he felt as he headed toward home plate to face this man, McCann was still practically trembling.
"It reminded me of my first major-league at-bat," he said. "It was the same feeling, the same magnitude. I couldn't really feel my legs."
Five months into his big-league career, McCann confesses he still has days when he stares into the eyes of some of these men he's playing against and wonders if all of this is really happening. But there are all those other guys -- and then there is Clemens.
Asked if he placed Clemens in a different category than any pitcher he'd ever hit against, McCann replied: "By far. He's greater than any pitcher I ever faced."
Sixty feet away, though, Clemens didn't have quite the same dossier on McCann. Asked how much he knew about this guy, Clemens didn't fake it.
"Nothing," he said. "Nothing, really."
But they both knew this was one huge moment in this game. And everyone in the park knew this was not a time when pitchers like Clemens let hitters like McCann change a game.
"A game like this, Smoltz against Roger, they're both going to do damage control, not let certain guys beat you," Biggio said. "And then one of those guys did."
Fortunately, the guy who did knew the deal.
"I was going to go up hacking," McCann said. "Pitcher on deck. Two outs. He can start throwing his dirtiest stuff up there. So I was definitely hacking."
Well, he hacked his way right into history. And when that baseball disappeared, this whole night became a blur.
Asked if he could put that feeling into words, McCann responded with a laugh.
"Well," he said, "I don't remember running around the bases."
And Clemens would appreciate it if he -- and all of us -- would forget the rest of this night, too. Clemens would go on to give up five runs in five innings -- one more run than he allowed on the road in April, May, June and July combined. In 31 postseason starts, his teams, incredibly, have now lost more games (16) than they've won (15).
But his legend is secure, no matter what he does from here on out. It's McCann's story that is just beginning.
Except McCann can't get rolling on the rest of his career until he recovers from the shock of what he did on the first October swing of his career.
"It had to take him all nine innings to come off Cloud 9," chuckled his teammate, Marcus Giles. "It might take all nine Saturday, too."
Jayson Stark is a senior writer for ESPN.com.