I think I've found a good example of a most famous master recorded on a partially erased tape. The Doors, "Light My Fire". At the very start, roughly 5 seconds in, a female voice says something like "appeasingly". It's heard most clearly in the single mono mix, and (less so) in the mono mix. Stereo mix has it as well, but it's really subtle there. This means, it's on the 4-track master. Though it was the mono mix that was paid the most attention by Paul Rothchild and Bruce Botnick, they weren't able to do much in mono.
There is also unique stereo remix from the 4-track master made by Steve Hoffman, on the Audio Fidelity 2014 release "Legends / Get It On". This subliminal thing is still there, but oh-so-subtly. (Haven't checked yet the "Perception" remix by Bruce Botnick, as I am aware that some subtle noises are cleaned there.)
We know now it isn't Carol, as she recognised the fact herself