Hi Patrick.

73643 actually says a few things to me, not just about the date (which I will get to, don't worry!) - it's quite an interesting number. No, it really is, don't all run away!

When the X (where X is Carrera, Camaro or Autavia) 30 models are first introduced, they use a Valjoux 7730 but the equivalent X 12 models continue to use the old stalwart Valjoux 72. This first happens around the tail end of 1969 or just into 1970. Less than a year later (it may be a little longer for the Carrera than the others, as there is a distinct generation change for the Carrera at this period), the 7730 (which is a very lightly reworked Venus 188, Venus having been acquired by Valjoux) is itself replaced by the 7733 (2 registers, no date) and 7734 (2 registers, date window at 6 o'clock).

With this change, the three register watches begin to be powered by the Val 7736 instead of the Val 72. I say begin, because if you bought a first generation Carrera 12 at this time, it would still have the V.72.

Now, how does this all affect the Camaro? In the brochures, we still see the three-register Camaros with a 7220 model designation, which means they are still using the V.72 too, just as the contemporary first generation Carrera 12s are. So at least partway into 1971, the Camaro is still using V.72.

73643 is a number we can easily derive:

73643 means it uses the Valjoux 7736 movement.
73643 means it's a Camaro.
73643 means it's steel-cased.

Deriving, because it never appears in a catalogue as far as I've seen. Camaros in 1971/2 are only shown as 2-register 30s, with Val. 7733 or 7734, though it is entirely logical that the contemporary Camaro 12 would now be V.7736 powered.

So, back to the original question. I think we're looking at a very tight time-scale for 73643, of somewhere from the latter half of 1971 through 1972. It's rare we can age a watch so precisely, but I'm pretty comfortable with that deduction for all the reasons above - if you could share the first three or four digits of the serial number too, it would be very interesting. And I think we'd all like to see some pics of these two Camaros, it's a model we don't see all that much of!