I have come across related info regarding this. Hand crank 99s doesn't always have the same hand wheel or hand crank as other models. I'm not sure of the details, but I guess it's related to early or later productions and machine size (case size?). My 1950 201K looks like it has the same hand wheel as your 99 does, sort of nine spokes in the wheel.
Do they have parts numbers? Industrial treadles have large hand wheels, and the older models like 15 and 27 can have very heavy thick hand wheels. I'm not sure about early model 66s, the early production after 1900.