These are the reserve numbers as used so far:
- All numbers used in 2014 have been maintained for 2015
- Red Bull have 16
So, we can assume the numbers were assigned based on the 2013 Constructors' Championship, thus the spare numbers were:
15/16 RBR
23/24 Mercedes
28/29 Ferrari
30/31 Lotus
32/33 McLaren
34/35 Force India
36/37 Sauber
38/39 Toro Rosso
40/41 Williams
42/43 Marussia
45/46 Caterham
Assuming only consecutive numbers were issued (this assumption would make the system work).
The only two of these numbers which have gone to a new driver in 2015 are 28 (Stevens) and 33 (Verstappen). However, we don't know if they were allowed to "steal" these numbers because they were picking in the close season, or if they were allowed to do so because the teams they'd "stolen" from hired 2014 (thus numbered) drivers as their reserves (FER: GUT/VER, MCL: MAG).
Also, Nico Hulkenburg, without you* Ferrari's reserve numbers would have been 27/28
.
Obviously, I hope that at the end of the season that all of the above listed numbers would be available to any person who had a thing for numbers between 29 and 46.
I have now thought about this way too much.
*Well, actually Jules Bianchi would have taken 27, which I suppose would have had the same effect in practice. So, in hindsight, there'd likely just be a whole lot more photoshop involving Gilles Villeneuve.