Large institutions had these capabilities since the 1960s. There were parallel universes like Tymnet and companies would set up first party networks using vendor protocols like IBM's SNA (which had a few precursors like QTAM). Users were concentrated onto large machines but machine to machine communication was equally important. This history and significance seems appallingly preserved.

There were even parallel universe packet switched networks by phone companies like Bell and MCI in the US.

The novelty of the ARPANet was that it allowed for the construction of a resilient open access network (Tymnet and various phone companies packet switchers were centrally administered walled gardens). Once the code was coupled to UNIX in the form TCP in BSD, it rode that wave and the sequel of "open systems" a few years later into ubiquity across all operating systems.

Yes as a former member of TEC (Tymnet Engineering centre) the whole OSI networking tech is poorly documented.

I remember running map reduce code on the largest(non black) UK PR1ME network in the 80's which was cool.

OSI's problem was it was designed in a world where each country would usually have a single PTT - in the UK it also suffered from not billing as an all you can eat model.

Tymnet existed into the 1990s at least. I used it for dial-up access to servers at work for remote nighttime support of batch jobs. I don't miss those 2am calls.

The auto assembly plant I worked in had SNA (active, but unused) in 2006.

Various circuit switched (ISDN) or non-IP packet switched technologies (SNA/X.25/Frame Relay) are apparently often used as backup links for various automotive EDI stuff for JIT ordering.

It was the uplink to the mothership for vehicle content broadcast. JIT was local DSL.