What's the history behind the numbering on relay terminals, as shown in the attached pic?
I'm guessing telecomms or perhaps automotive?
What did the other numbers get used for?
I to have wondered that. Its probably automotive because those relays are usually found in auto applications. No idea what the other numbers are but there are several things out there with funny numbering .
With Google by my side I found this which seems to be a master list of every connection on every device in a car, at least when the list was drawn up.
So yep, those numbers are automotive.
I would speculate that there is a much longer list now, for airbags, parking sensors and the like.