As far as I know, those were not the points of the joke.
I noticed them for the first time yesterday too, after not noticing them for decades!
As a teen, I'd printed it out, pinned it up on my wall next to the Cray-1 centerfold, and scribbled a bunch of modem phone numbers, user names and passwords all over it, and never even noticed.
I did a quick search for other A's and B's and found that it used those characters as much as any other character for shading, but that sure seems like something some mischievous student, lab member, turist or sentient TECO script at the MIT-AI Lab might have done.
There was no file security so anyone could have edited them in.
Maybe one of Minsky's grad students was performing some A/B testing or eye tracking experiments.
Somebody should ask RMS if EMACS had some special mode for editing line printer porn.
NSFW: MS C0LLINS - 0UI - FEBRUARY 1973: http://its.svensson.org/HUMOR%3bVICKI%20BODY
https://en.wikipedia.org/wiki/Grandfather_clause