: 1. When did Heuer switch from the Made in France dials to the Swiss
: Made dials? Was there some overlap?

It looks like there was. I was dubious at first over some Heuer dials that have Swiss made at the bottom but Professionel written the French way. Are they genuine or not ?

: 2. When was the ETA 2872 movement introduced and the FE 4611A
: movement finished?

Again a weird thing as per note 1 as I have seen monnin with both

: 3. Was there an overlap between French and Swiss production?

There must have been a point when both houses were producing as Heuer must have given notice to Monnin which would have included a certain amount of watches by both houses.

: 4. When did the case backs for the orange dial examples get stamped
: with the catalogue ref. 980.005 (or is there something 'wrong'
: with a France orange dial and a 844 case back on the same
: piece?)

The 005 is obviously the Swiss monnin the 844 the French

: I will try to post some photos in the coming days. I would be
: interested to compare notes with other early era 844-type dive
: watch owners out there.

Now I have multiple variations of monnin. Some without red numerals so a black normal dial. Some with cathedral hands. Some with different bezels. They were obviously trying to find what looked right for the watch at the time or was it simply a parts bin exercise?
Some casebacks are stamped 844 and some are blank. I can't discount them as fake because no one really knows.
Also I've seen non heuer 844 with 844 case backs so was it simply that any customer received a serial so the list of serials includes other branded 844 ?

Thanks to a good friend I even have a possible orange quartz proto dial which isn't stamped Heuer but no doubt would have been.

I've been very lucky to be able to have and have passed on so many monnin. They really are special. May be time to shift a few soon to go down another route as I did with Autavia. Time doesn't stand still unless they are stuffed in the safe:-)