I have never collected by factory. I had no idea, but I just looked at the nearly 600 T206s I currently own.
F25 - 3
F30 - 8
F42 - 9
F42OP - 12
also one overprint with no factory number that I can see
Edit: The factory # was hidden because the overprint is a little off center. Had to blow up it see it. Another 42.