Out of the four M54's I have, none are upside down, BUT out of the 29 US 37mm rounds I have, M16, M17, and MKIIIA2 cased rounds, I have an M80 AP-T 1942 dated and an M51B APC-T 1944 dated that are stamped upside down, so it's not common, but not unheard of. You get someone new on the stamping line that's just trying to put production out, the supervisor's not going to QC down check a round for improper stamping, just tell the newb to pull their head out and do it right 'cause we need to get rounds to our boys the best and fastest we can. Cheers, Bruce.