I’m always afraid when I hear someone copypasting Apple memos. Obviously they must have watermark, if not text glyphs (rn = m, and further UTF-8 incantations), at least subtly different phrasing depending on which department, or person, views it.
However it's true that the top invisible scanlines normally used for Teletext could have been used for this. My VCR did record them, I was surprised to be able to view Teletext pages at the time of recording, though they were full of distortion.
It would have been possible to filter that out though.
I think at the time VHS recorders were still mostly analog and would have been recognisable from their artifacts the same way a typewriter can be identified once found.
The mechanics of how they worked are actually pretty interesting, I highly recommend Technology Connections' video on the subject [1], as well as the one on closed-captioning [2] (and his series on analogue TV in general [3])
[1] https://www.youtube.com/watch?v=KfuARMCyTvg
[2] https://www.youtube.com/watch?v=6SL6zs2bDks
[3] https://www.youtube.com/playlist?list=PLv0jwu7G_DFUGEfwEl0uW...
No schools in 1987 had color laser printers with this technology (and I doubt many businesses did either). Any students trying to do something fishy would have had to make do with, at best, 24-pin dot matrix printers with color ribbons.
