I just bought an original Macintosh and the mouse is not normal in one way; it has the cable and connector from a LISA mouse. I've asked for more and better photos of the mouse/serial labels etc. from the seller prior to them shipping it to me but for now I just have the attached images. I've also added a LISA connector image for comparison.
Sadly it was a donation and I can't ask any questions of the original owner.
My guess is that the mouse had the cord replaced at some point and given the rarity of the LISA cannot understand why this was the replacement used. I'll open the mouse up when I have it and see what's inside.
Maybe the build date is in 1983 and it's something special like my week 2 1983 keyboard.