Then, as now, most long distance calls were to nearby points to which the operator had direct trunks or on high-traffic routes to which operators also had direct access. If they needed routing information beyond that it was on the keyshelf (which had the great majority of the remaining routes shown) or on the keyshelf bulletin which had hundreds or thousands more routing instructions, well designed for very quick access.
The percentage of calls which had to go to Rate & Route was only a very small percentage.
Carrier systems, and before that phantom circuits, were in general use well before the 1930s. In the 1950s, living in Oklahoma City, I found a Bell Labs Record or Bell System Technical Journal article describing "The Fourth Transcontinental," which was built in 1935.
It was of special interest since the fourth "transcontinental" started in Oklahoma City and extended to the West Coast. From the East Coast to Oklahoma City by 1935 the toll network was so dense and of adequate capacity that there was no construction needed east of Oklahoma City.
The article went into detail as to what building it started from in Oklahoma City, the considerations in routing the cables out of the building and down what streets, and eventually to the actual originating carrier system on SW 89th Street, with a photo of that building.)
A new carrier system, I believe designated L carrier, was used on the open wire pairs from that building to the next repeater, the next, and so forth to the West Coast.
Carrier systems were designated alphabetically, and while some never saw any use, L is pretty far down the alphabet to consider carrier systems as being developed in the 1930s.
Wes Leatherock snipped-for-privacy@aol.com snipped-for-privacy@yahoo.com