The Invisible Dollar
Two brand new $1 bills are stuck together. The mint doesn't catch them, so they are sent to the bank counted as one, then the bank teller doesn't catch it and they are handed out as one, then the recipient doesn't catch them and they are spent as one, then the cashier doesn't catch them and gives them out in change as one, the new recipient doesn't catch them and places them in a savings jar as one, the jar then sits for years until it, and all of its contents, is destroyed in a house fire.
So, did the second $1 bill ever actually exist? Does it depend on context, whether counted physically or economically? If they were effectively just $1, which dollar existed and which didn't?
What does this mean for other things?