Hi olup,
I am curious, do you happen to be known also under a different alias on this forum?<- wiped out.
Partial update and "fast partial update" aka differential update are not the same.
Almost all controllers support update of partial windows of the screen (not the 1.54" 3-color 200x200).
Only controllers of pure b/w e-papers can support differential update; they need double buffer for previous and current content. The controller of the 7.5" and 5.83" does not have double buffer, as it supports greylevels instead (the big parallel interface e-papers with DESTM32-T e.g. has differential update for pure b/w content, but this does not work with grey level content).
The 4.2" b/w is a special case: the controller supports differential update, but originally no waveform table for fast partial update was available.
See also:
Good Dispay ePaper for Arduino #133
Jean-Marc
PS: thanks for the question, I need to bookmark this post!