I've seen several of the Rhoades with the mark there was one with a sliver of the mark in a recent REA auction they are definitely not factory numbers.
I don't know why the factory numbers are only found on print group 1 subjects but the T206's were printed for close to two years so I'm sure there were changes and maybe
they came up with a different method of identifying the factory's on the sheets if that's what the numbers were for.
here's the one that was in REA, I bid on it but I wasn't willing to pay a premium for it because of how little of the mark was present.
https://bid.robertedwardauctions.com...e?itemid=96739