Since Hatton's are dealing with the factory directly, it wouldn't surprise me if they've agreed an overall number of locos, but can adjust the numbers of each one depending on the pre-orders. So the more popular ones will see more produced.
Its something I have wondered about, and don't think we will ever get an answer to the quantities made. In comparison-Hornby will do runs as low as 250 (used to be 1000), Bachmann 504 or 512 and ViTrains did as low as 150 and Olivias had 2000 Class 58's split over 8 locos.
There are a few "base" liveries - EWS, FL, F/L Powerhaul, DRS Compass, DRS plain, GBRF, GBRF Europorte, GBRF Barbie, Colas, etc. and then after that its just setting up tampo printing to make each loco's finer detail.
Effectively, there may be say 1000 EWS models (not bringing wing/no wing mirrors into equation!), split over the range to do the EWS & EWS DB's. After that its then differences with tampo printing for each model.
Like I say I don't think we will ever know the exact amount of each model produced.