Basically, Heuer gave the first generation Carrera a "facelift" partway through its lifecycle, in much the same way as carmakers do to keep a model fresh.

First execution 2447 N, with the features you described on your watch:

And second execution:

Personally, I find the second execution loses some of the Bauhaus simplicity of the first and some of the additions are just for decoration not function, but a lot of people like it as it introduces "panda" dials (i.e. where the registers and dial have contrasting colours).

How much you wind it depends on how you wear it. Many of the people here have multiple watches, so an individual watch is often left to wind down completely. Whilst you wouldn't want to leave one like that for too long for fear of something seizing, it doesn't do any harm. Equally, the watches were designed for daily wear (rather than us weirdoes with many watches ;) ), so keeping it wound shouldn't present too much of an issue either. The Valjoux 72 movement is a veteran movement and had been refined over decades by the time it was used in the Carrera.