In my old neighborhood of Philadelphia, the service was split. All 0+ and coin 1+ calls went to a TSP (the older type) facility which handled a large section of the city. But this facility did not handle plain 0 (zero) calls for some reason. My neighborhood's 0 calls went to a suburban CO that had cord dial-assistance operators. (I don't know where directory assistance calls went, that was another office altogether).
The Mountain Bell history ("to Laser Beams") shows pictures of cord boards with some upgrades -- modern illuminated keypads on the keyshelf and little computer terminals. The Bell System did a lot of such improvements to legacy technology to improve efficiency without a full formal upgrade; the Bell Labs Records of the 1970s were full of articles about that kind of thing. Some Step by Step offices had computerized front ends and back ends to help route and charge calls, in some cases becoming a poor man's common control system. (That is, the dial pulses no longer operated the actual Strowger switches but rather were recorded in a computer, which then directed the Strowger switches.) This sort of thing was necessary to expedite higher calling volumes in growing suburban areas and automated toll and operator services.
A look at small town telephone directories of the 1960s showed dialing was both limited and cumbersome in many places. To reach a neighbor- ing exchange, one might have to dial a special prefix, and a different prefix for each area, as well as from where you're calling from. The charts could be rather complex. Or, you could only dial your own neighborhood and anything and everything else required 0.