Re: Hmmmm...
outside ARPANET (and possibly early versions of JANET) it wasn't really used
I don't believe that's true. While other protocol families such as DecNET, SNA, and XNS were also still common at the time, even in the first half of the '80s TCP/IP had a significant share of local networks and small-i internets in academia and some businesses. The CMU/IBM Andrew Project was always TCP/IP-based, for example, and it started in 1982. The same was true of MIT/DEC/IBM's Project Athena, which started in 1983. I think BSD 4.1a with TCP/IP came out in '82.
For the big-I Internet, besides ARPANET there was CSNET (routing TCP/IP over X.25, starting in 1981), NSFNET (1986), and others.
Wikipedia says JANET (an X.25 network) didn't start routing IP traffic until the 1990s. BITNET, a prominent US academic network, and IBM's VNET (the largest internet in the world until it was surpassed by the TCP/IP Internet sometime in the '80s) ran on RSCS, a pre-SNA IBM protocol. RSCS was a store-and-forward protocol somewhat like UUCP.