u/Lanky_Creme_7696

Hello all, I’m trying to understand these serial numbers but it’s not working how I thought it was supposed to. I thought the first number was the year and the second two were the month but that doesn’t seem to always work? The screw back seems to work, year ending in 1 and the month of April (04)? But the other two you end up with a month of 30 and 90 haha. There’s obviously a different format I don’t know. Thanks for any help ☺️