Mavimao said:
I’ve always thought that the 1978 and the 1983 versions are the same.

I once came across “proof” of the opposite (although I didn’t know it at the time) when going through a bunch of old, recorded TV broadcasts on Beta tape. In the space between half-hour sections of the tape, there was one recording partially over-writing the front end of … THX 1138 (full-screen). I didn’t think much of it then (the tapes were full of re-tapings) but wondered when it was. Playing a bit of it found a station commercial for the 1984 Super Bowl (or some other, annual sports event).

More important is that the SEN & children scene was complete, even though GL’s 1983 version (now for TV and commercial videotape & laserdisc) had that scene edited-down. (NOTE: that means George Lucas himself cut it out for the 1983 release, as I once speculated in the original THX 1138 thread.) The 1984 Beta-tape TV broadcast was GL’s 1978 release (only for theaters & TV stations) that was still broadcast into 1983+. Years later recordings on other TV-recording tapes had only the edited-down scene. Clearly, all the stations had the updated (edited-down scene) movie by then and showed nothing else.

I’ll track down that tape again to glean addition details, now that we have more and newer information.