In the link you pointed to shows that by summer of '80 there was no longer support for softkeys and there was support for a mouse. The primary documents at http://web.stanford.edu/dept/SUL/sites/mac/mouse0.html only start talking about a Macintosh mouse in spring of '80.
This fits well with a transition from Canon Cat UI to a PARC-derived UI, as you've described.
Now that I am paying attention to that, I see in Jan. 1980 Raskin wrote "A lightpen for graphic input is being considered" for the Macintosh. http://web.stanford.edu/dept/SUL/sites/mac/primary/docs/bom/... .
In the link you pointed to shows that by summer of '80 there was no longer support for softkeys and there was support for a mouse. The primary documents at http://web.stanford.edu/dept/SUL/sites/mac/mouse0.html only start talking about a Macintosh mouse in spring of '80.
This fits well with a transition from Canon Cat UI to a PARC-derived UI, as you've described.