Yes, many things here I should be doing more of, thanks:

(1) UML is something I haven't been doing much of, I will try to use some sequence diagrams and other things, that could be useful

(2) a table to layout all the variations of the variables and what the output should be with "don't cares" to cut the options down - I'll experiment with this

(3) black box abstraction - True OO I guess... I'll look into it

I've tried ChatGPT extensively, but it never produces anything remotely useful, since mostly I want to document the "why", not the "how" or "what", if that makes sense

Thanks for the input!