Maybe the sizes of the griddles was chaged to fit changing sizes of stovetop burners (if they did change in size). There was a later series of rectangular griddles, and not just the No.8 size, that were shorter and wider than the earlier series. Probably produced starting sometime in the 1940's. BTW, the small TM is not really a block TM. Block refers to the "blocky" style of the letters on the large (block) TM and the small TM lettering is not blocky but more "typewritery".
Steve