All my research shows that first execution 2447 Ds have the blue deci scale without the scale being cut into, thusly:

Second execution watches have the black scale, again without the register cutting into the scale:

I don't know about seeing three watches with the cut out, but I have seen that self same watch up for sale at least four times over the space of six months or so, sometimes with the sales completing, sometimes being ended. I would just be a little wary of something I wasn't quite familiar with.

The colour of the track does vary, earlier watches being a very distinct silver, later watches merging more with the dial, as this Tachy comparison shot shows:

You'll notice that, even though the track base differs between the watches, the printing and size between the two is effectively identical. I would expect the same to hold true for the Decis (which we see less of than Tachys), but I'm not sure of the one with the register cutting the scale. Could well be a redial as Shaun suggests, but not beyond the realms of possibility that it's original too (Shaun's option B) - I'd like to see some higher quality close-ups of the dial really.