I've seen maybe 10 second generation Carreras with deci scales now, in two variations (numerals on inside or on outside of the scale), so I'm happy that it was available from the factory. Unlike the first generation, where versions with different scales were distinct models (2447 T, 3647 D etc), the default appears to be the Tachy bezel, given the vast preponderance of that bezel version. Best guess then is that the Deci scale was available to special order only.

Quite why someone would need yachting markings AND a deci scale is beyond me, but maybe a sailor amongst us can shed some light on it! Or perhaps it's just that the original purchaser liked the look of that combo and you can't really blame them for that.