Twisted:
Yes, if you wanted a single CO line to ring on a 1A2 station, they you could wire that line directly to the yellow-slate pair of the station cable. But, if you wanted multiple lines to ring at the same set, you had to use the internally-generated ring cycle and voltage. This is because if you tied multiple CO lines to the same ringer, they would be effectively tied together.
Internal ringing also created the flexibility to have various combinations of lines ringing at different stations by using a diode matrix to isolate common ringing for some stations. For example, three lawyers all had their own two lines that rang at their station, but their common receptionist had all six lines set up to ring on that station.
Oh, yes OBTW. I remember many sites like you mentioned. We used to service the Kennedy Center in Washington DC that had hundreds of lines, even more stations and lots of mixed ringing. They had lines coming from cards in multiple closets backfed over house cable, lamp extenders, you name it.
It really got fun when there were transfer keys involved. As if the matrix wasn't already confusing enough!
