The blue highlights are down to it being a perpetual calendar, which those other two aren't.

Perpetual calendars were a long running line for Heuer, but they were often making detail changes to the design. Nothing screams out incorrect about Amran's example; not many other companies were making triple calendars at the time, but we do sometimes see a name change on the dial to add value. This one looks like Heuer to me.

Your partner has good taste, but he hasn't made your life easy - we know so much more about the watches from the 60s and 70s :) I'd put this one around the decade change from 40s to 50s.