I've just purchased an early Carrera 2447N and would like to try to narrow down the production date (without trying to open it up). I can't seem to find a good online resource that really goes into the details of the Carrera, and I was wondering about a few things.

First off, my watch has the narrow double-hash mark at the 12 o'clock position; from what I've been able to gather this seems to indicate that it's an early model. Is this true?

Secondly, the crown on my model does not have the Heuer logo on it. It's not a hex caseback model though.

Finally, in the chronograph hours register (at 6 o'clock) there's a little T above the lettering "Swiss" - I wondered if this could narrow it down, as there are many photos of 2447 Carreras on the internet without this T.

Any help (or links!) would be greatly appreciated!