When it was first introduced, in the 50's, the QO family of breakers only went to 60A. The Q1 family went from 70 to 100A, the Q2 went from 70-225A.
The QO has hardly changed since its introduction. Around 1980, the higher ampacity (70-100A) ratings were introduced.
The Q1 family was twice as wide as the QO, it spanned the entire width of the panel, which is one reason that 54 circuit panels existed during the time that the NEC limited the count to 42 circuits. It was dropped when the higher ampacity QO breaker became available. The only unique device was the plug-in Q12100TF main breaker design, where the lugs were on the side of the breaker.
The Q2 family was never designed to plug-on to the same bussing as the QO family. When paired with QO its purpose was primarily as a bolt-in main breaker.
The QOM1 effectively replaced the Q12100TF, although they are not interchangeable.
The QOM2 effectively replaced the Q2 as a main breaker in QO loadcenters, but it too is not interchangeable.
