I had a linear stereo VCR (With Dolby noise reduction) long before I had a hifi deck. The linear tracks on every stereo movie I had from that time were stereo. I'm guessing that a mono vcr or playback through the antenna outputs simply downmixed the sound? (Damned annoying that modern decks don't have linear stereo playback for older tapes.)
Some studios didn't want to pay extra for the use of the Dolby Surround logo, which is why a lot of older video titles simply say "Stereo Surround" even though the movie has a Dolby track.
I was puzzled back in the 80's as to why old four channel quadraphonic amps were flying out of local thirft stores until I learned some early home theater buffs were getting them to decode the surround tracks off of laserdiscs.

Originally posted by: Neil S. Bulk
Mono compatible on VHS tape meant it had a mono linear track in addition to the stereo hi-fi track.

Anytime a matrix Dolby Stereo soundtrack was transferred to a stereo video format, the surround track was carried over, simply because of the way Dolby encoding works. Every stereo signal has an out-of-phase component, which is how Dolby Stereo was encoded.

Neil