Regarding Appendix C: How accessible was the maintenance manual? Was this strictly internal to IBM and (maybe) licensed contractors or would this have been public (e.g., general available on request)?
Regarding Harry Katzan Jr, the book is really all about the user’s perspective and how to operate the machine with hardware mentioned only as far as it concerns normal operations. This could have been due to some kind of non-disclosure agreement, but, on the other hand, there isn’t really any “need to know” due to to how the book addresses its subject in general.
(Personally, I’m speculating that IBM was kind of ashamed of the PALM processor, as this may have been perceived as some kind of taint of a subpar, cost-cutting engineering solution — while it was indeed an ingenious abstraction. It may have also been that there hadn’t been any definitive business decision regarding whether or not to open this to 3rd parties. So better don’t talk about this…)
*) Edit: Regarding IBM being ashamed, I find the story of the IBM Aquarius, one of IBM’s several attempts/concepts towards a personal or home computer in the 1970s, quite fascinating: This concept had proceeded to a series of fully designed and functional engineering prototypes and relied on a software ecosystem that would have come in ROS on bubble memory cards. Last minute, concerns about rare failures of bubble memory had been raised and the project was subsequently canceled. Nowadays, this would have been a non-issue for a consumer product: just exchange the few faulty cards and everything is fine. However, the mere idea of having an unreliable product (and should it be unreliable just in theory) seems to have been perceived as an unbearable taint on the engineering reputation… We may consider that anything personal computing was still more like an experiment, not worth endangering the core business in any way. I guess, the same is generally true for 5100. (So, “let’s do this but don’t talk about it”, may have well been a possible scenario.)