Edison 2/4 conversion pulley assembly differences

[pughphonos]

Hi All --

There is no end of learning about Edison Home phonographs!

Edison's light bulb went off for me today on yet another issue. The left half (pulley side) of the 2/4 gear assembly I assumed UNTIL TODAY was always a "female" with four holes--onto which the other assembly side (with two "male" prongs) inserted to spin for 2m records. Whenever I pulled apart some model Bs (and found prongs on either side of that assembly) I just assumed that some hobbyists had mismatched the two parts.

What I seem to have learned today (and I need to be confirmed in it) is that the Edison model B (and I assume the A too) 2/4 conversion assemblies had prongs either side that hit and held when pressed together for 2m mode--and the four holes on the pulley side were not introduced until the model C.

Have I learned correctly?

MP