Unsure of your question Uppo?

A and B base refer to dispatching schemes. They are basicall identical, except A base was used mostly on touch button systems, and had multiple diagnostic cards you could plug into the card rack, and B Base was used with regular push buttons, and had one diagnostic board.

Both were based on VIP 260 logic, but transferred from relay form to DTL logic. (DTL = Diode Transistor Logic)

And to confuse things more, there was a CB base. Basically a B base dispatcher, but additonal boards that read flags in the hatch for Selector functions. Basically the 1st Otis that I'm aware of that did not have a mechanical selector.