It is a very confusing case so little details are easy to miss. I have to admit that when I was recently doing some archival work, I was noting to myself how easy identity theft must have been 'back in the day'.
I was thinking the same thing. It would take forever before you noticed. I remember working at my uncle's pharmacy one summer and having to check the credit cards in one of those books they would send every month. This was around 86 or 87.