Reskins' Appearance In Service Mode

How is it determined when and how often reskins appear in service mode, and is it possible to control this?

I ask because I downloaded the IC2 Dosto reskin and the coaches appeared mixed in with Regio Dostos - which isn't apt, and this sort of thing limits the reskins I download

 

its random I believe. There's no set pattern as far as I am aware.

Hentis.

 

Just as I suspected. This works really well for some, not others