@kentpitman @ldbeth @kim The first TECO ran standalone on an MIT PDP-1. In 1964, it was ported to the AI lab PDP-6, also running standalone.
In 1966, Bob Clements brought TECO along to the Stanford AI lab and ported it to their PDP-6 running the DEC Monitor timesharing system. From this rather early and crude TECO stems all DEC versions.
Back at MIT, TECO was updated to run under the ITS timesharing system and there was a frantic development, culminating in EMACS.