This was a good read! I particularly enjoyed the “great point, header 2” quip :-)
I mostly use Org mode’s tables for my spreadsheet calculations, so I wanted to find out what it uses. I think it’s something like the VisiCalc algorithm: https://code.orgmode.org/bzg/org-mode/src/master/lisp/org-table.el#L2876-L3044
I think this makes sense as the spreadsheet is in plain text, and recalculations are triggered manually. I don’t think it’s possible to tell which inputs changed since last calculation.
An excellent article, good find and/or good work if OP is also the author :)