Just joining this group today because of this post I came across while trying to figure out the date of my 45-70 as well, which I now know is a 1972 model. Going by the formula of subtracting the first two digits of the serial number from 100 wasn't making sense because I always thought the first number was a B but then just figured it was a worn #3 die in the stamping process or something so assumed it was a 3 but then that wasn't making sense either because that would have made it a 1970 which after reading your post makes that impossible. So BO it is!👍
