[al8apex]

I believe that each office had a supply of plates to work with

"back east" you used to be able to tell what county the plates were issued from based on the prefix letters. I assume each office was given a large supply of plates to issue from and there must have been some sort of "regional" issuing office that serviced all the dealers in their "territory" that is why you will see some plates with a "later" letter prefix that may have been issued before and earlier prefix

best guess here