[tmiller6]

What little I know is that the plates had a third, smaller size when there were only 5 digits. Prior to the SAE standardizing the North American License plate size, issuers could do practically anything they wanted as far as the outside dimensions. The '31 plates were an exercise in economy where they stamped them out of a thinner gage of metal. In previous years, I believe Michigan issued a Diamond M symbol on the plate when they exceeded a million registrations.