Yes, at the time the only real theoretical bandwidth requirement was the highest audio frequency they wanted to be able to pass, since this was all a trivial an

Yes, at the time the only real theoretical bandwidth requirement was the highest audio frequency they wanted to be able to pass, since this was all a trivial analogue setup. In practice there were a surprising number of extra constraints, some things you'd expect like the rolloff of the filters and amplifiers, but others are the kind of thing that only come up when you have very long cable runs with hundreds of amplifiers... they had to think very carefully about how specific harmonics would accumulate through all the amplifiers and place carriers accordingly, so that the harmonics that accumulated to a significant degree would fall in unused frequency ranges. All of this tended to increase the practical bandwidth requirements, or in other words get you fewer channels than you would expect on a given cable. A sort of interesting issue is that the worst crosstalk problems were always at low frequency, so most of these carriers operated entirely above audio frequency. The audio frequency was thus an available circuit, but the quality was poor, so it was usually used for order wire or other internal purposes. This had the very convenient property on many open wire and cable systems that a lineman could connect their butt set directly to the pair and use it to call an exchange troubleshooting desk, the butt set didn't need to have any awareness or support for the carrier technology since the AF band was otherwise unused. This is very similar to how DSL works today.