> The "single buffer with invalidation" model of Win16 (I cannot remember how it works in X)

Same way, they both come from Macintosh (which, if i remember the apocrypha correctly, was Bill Atkinson's idea based on what he thought Xerox Smalltalk was doing even if it turned out it wasn't working like that).

You remember correctly:

https://www.folklore.org/On_Xerox,_Apple_and_Progress.html

https://www.folklore.org/I_Still_Remember_Regions.html