Question about USN dog tag find at flea market

[Tonomachi]

I found this USN dog tag at the flea market yesterday. It had an ugly glob of solder on the back which I probably shouldn't have removed but it was too late once I thought about it which revealed a thumb print. I then noticed that the original tag was stamped USNR but someone had scratched out the R. So I was curious as to why someone would want to cover up their thumb print unless it wasn't their thumbprint. So my question is did they reuse dog tags that maybe already had the thumbprint but was tossed into a box before being stamped. I was wondering under what circumstance this would take place. Any ideas?