...when confronted by an unfamiliar watch.

Separate the watch out into individual elements (e.g. markers, caseback, script) and then look for precedents with other Heuer models. And remember, individual components were often made by specialists and supplied to several manufacturers so most of the time it's not just similar to another Heuer you're looking for, but identical.

Once you've done them individually, you can roll them up and see if they confirm your initial impression of the whole. It works well in the field too - you don't need a photographic memory of every Heuer model but if no element stirs strong recognition, then just walk away.

In the early to mid 70s timescale, possibly later, for this watch, remember that pretty much every civilian Heuer was part of a named series too. "Unnamed" watches are generally an immediate red flag that needs looking at.