I don't disagree that there was significant malleability in nomenclature, but the idea that zero-pages or 9900-style workspaces were register equivalents was in

I don't disagree that there was significant malleability in nomenclature, but the idea that zero-pages or 9900-style workspaces were register equivalents was in the most charitable sense was never anything but marketing, and never by anyone who honestly did the math. Even the 9900 folks pretty quickly stopped trying to convince us they had 'registers' and moved to how quickly they could change contexts and mitigate the speed asymmetries between on and off chip memory.