SxS offices varied greatly in size, complexity, and service features. The Bell System history describes several ways long distance trunks were tied into an SxS office, such as whether digits were held and then passed on or perhaps a high speed trunk immediately ready to collect the long distance number. Trucks between offices themselves evolved with technology.
Some SxS offices were remote and all special needs (operator, repair) had to be handled elsewhere, some were larger and had in house facilities. This obviously affected trunking for such needs.
Some SxS offices got some front-end or back-end electronics in the
1970s to give a little added push to the system.Compounding the problem was that many SxS offices used five digits for local calls and used absorbers. Another issue was future growth, which was generally high in suburban areas.
Other complexities were ANI and Touch Tone.