It's hard to put an exact date on Ron. Crowns are such an easy item to exchange that it can be difficult to pinpoint exactly what is original.

Take those Dato 45s for example. We're all agreed they're unsigned, but we still see examples with Heuer crowns, so the winding stem for an L189 is either a natural fit for one of the other movements too or can be bodged to fit into such a crown with a little bit of glue.

We see a fair few first gen Carreras bearing 5.9mm signed crowns too. Those are Cal 11/12 crowns that have been fitted/made to fit.

The only conclusions I can draw with confidence are:

- watches with S/Ns as low as yours should indeed have unsigned crowns
- the likelihood that a Carrera had a signed crown ex-factory increases with time
- by the time of the second execution watches, every watch should have a signed crown
- any watch with a 5.9mm diameter crown has had it replaced
- equally any watch with a thick or even very thick crown has had it replaced from another Heuer model - Carrera crowns are notably thin
- any Carrera purporting to be from 1962 or '63 has jumped the gun!

There's not necessarily complete agreement over crowns: http://www.chronocentric.com/forums/heuer/index.cgi?page=1;md=read;id=37513

I guess to generalise, you can be happy with either signed or unsigned crown on a first gen, first execution Carrera provided it fits the correct dimensions.

It kind of goes back and forth on Carrera crowns, so here's a rule of thumb guide for those looking to buy:

First generation, first execution watches (e.g. 2447, 3647 etc) may have a signed crown.
Dato 45s should not have a signed crown.
First generation, second execution watches should have a signed crown.
Second generation (e.g. 1153, 1158) watches should have a signed crown.
Third generation (e.g. 110.573) watches should have a signed crown.
Fourth generation (e.g. 371.253 Twin) watches should not have a signed crown.
Fifth generation (e.g. 510.511) watches should not have a signed crown.

For anyone not sure on those generations, you can cross reference the model numbers given with the Carrera table on the MOAT:

http://www.chronocentric.com/forums/heuer/index.cgi?page=1;md=read;id=37513

Or reference this photo, which has the five generations from left to right: