The usual reason a reader might be unhappy is that something they wanted to see isn't there. So the solution is put in as much as you possibly can ;). Maybe future editions can be bigger and more comprehensive. OTOH there seems to be quite a lot of what amounts to implementation tutorials. Maybe that's not needed in a history book. In a history book I'm more interested in sources than narrative. Although, some interviews with important Lispers would also be cool.

I can understand not wanting to put in too much math and theory and that's fine. I can't really tell what is there and what isn't beyond getting some hints from the bibliography entries.

This (by McCarthy) showed up immediately when I searched for something unrelated, some articles by Jeff Barnett about Lisp 2: http://jmc.stanford.edu/articles/lisp/lisp.pdf

This is a link dump about Lisp 2: https://softwarepreservation.computerhistory.org/LISP/lisp2_...

I have been wanting to look into Lisp 2 because it had supposedly had an interesting trick in its GC. It was a compacting mark/sweep GC but had an antecedent of generational GC where it usually wouldn't bother trying to reclaim memory that had already survived compaction once. I've been interested in re-implementing that trick in some modern implementations for small MCUs.