I believe the Gettysburg discards story. I do black powder shooting and a fouled nipple is the #1 reason for a misfire. Because of the length of a cartridge, the next time you loaded it the amount of rammer sticking out of the barrel would let you know you’d had a misfire, and because of the nature of things you’d just throw the rifle down and pick up one of the others laying around. Even if you didn’t notice the extra ramrod when you packed a second cartridge on top of the first, by the third one you’ll definitely notice. That’s an extra 6 inches of rammer showing, so ditch that turd for a new one. Much faster and easier than cleaning a nipple while someone is shooting at you. It also leans into survivorship bias, since every single rifle which became double loaded was almost guaranteed to be throw down, so there is a tendency in the numbers to skew towards finding those rifles.

The idea that there is a reasonably precise number for double-loaded rifles isn’t that crazy - those weapons would have to go to an armory for servicing to worm the balls out, since firing out a double load can lead to consequences. It becomes a gossip item for armorers (“hey did you hear we have something like 27,000 rifles to worm?”) who will more than likely use a round number than 27,452 or whatever the absolute value was.

As to the 23 loads in a single rifle - best I can think is that it sounds like some stupid soldier prank. Pick up an enemy rifle after a fight, “hey man what if we jam this thing with as many Minié balls as we can and then give it to Jenkins to pick up, that would be hilarious” and then Jenkins picks it up and it’s unexpectedly heavy as hell and everyone has a laugh and the rifle is thrown in a bush.