номер плоскости?

[sss]

The colour of digits, its style and place where digit(s) was painted were the distinguishing features in this case
Also colour of the vertical tail (so-called peelotka) - which is absent for all your examples - may be useful additional feature

But it's impossible to recognise the regiment with the aid of these infos ONLY - you always need to know area (where photo was taken) at least. It will be better if you have the date (even approximate)