One of the things I found was that the larger octagonal commission plates were used up into the TS18000s, then it was a “clipped” plate in the TS18000-19000s, then by the TS20000s, they used the smaller rectangular plate through the rest of production. The reason for clipped plate had to do with removal of the patents displayed below, according to the UK TR Register. My TS20447LO has the later rectangular plate. I also have four rivets, my commission plate is held on by the bottom two and AFAIK, has never been removed. Sorry, I don’t have access to my files, so I can’t be more specific.