Okay, I was going off an old comment from Animats where he said "The Bravo file representation was plain text, followed by a control-Z as an EOF, followed by the formatting information. The compiler just stopped at the control-Z."
> So ^Z is a case of convergent evolution.
More likely common ancestry, no? DG RDOS also used ^Z to end input (not sure if it was stored in the file); also PARC built their own PDP-10 clones.