Yes Mike,
You are absolutely correct, at least someone else does their homework. But I never considered DS1 in "data" terms the way it is used today, even though it falls in that category, and Digital Data Service (DDS) was the upgrade to analogue private line data service. Those are the only RJ designations, RJ48C, RJ48X for DS1 service and RJ48S for DDS, that are data related. Those were the last RJ assignments from the FCC. The Bell System was still being difficult with CPE at that time, and they even got the FCC to do this affidavit nonsense, if you were going to provide your own CSU on DS1. Luckily, I never had to do any affidavits in the early days. I worked for an RCC, and we were able to wiggle around that stuff.
....JIM....