​Need to ask someone like Doug or Steve - but I thought/IIRC the moniker was because it was the compiler an end user got when you get the typesetter code.   ​That said, you have to be right in that it was the typesetter work that seems to be the forcing function.  As for dating it, it has to have predated the "white book" because we had the typesetter compiler at CMU before Ted Kowalski showed up for his OYOC year which I'm pretty sure was '76.

He had brought UNIX/TS with him and a xerographic copy of the white book proofs.  We had been running 5th and then 6th edition in '75 - when I started hacking.   Ted updated us to his system and that spread everywhere but the two CS IUS and SUS (image and speech understanding systems). 

I believe that I can date this because IUS and SUS had a special CMU 11/40e microcode (csav and cret instructions) and hacked typesetter C compiler, which was different from what Ted was using (which was even later).   So these systems could not use Ted's new kernel until someone in CS brought the two compilers in sync (Dan Klein maybe??) - I remember is was a pain in the tuckus because you could not take a binary from the CS systems and run them on the EE Dept systems.  But the CS system had more disk than we did, so they had all of the sources from outside places like MIT, UCB, et al on line.   We I was grabbing tools from those systems to update the EE systems and pushing what we wrote back to them.

Clem