Thanks Chris. The abreviation, Ausf., is more or less what we'd call 'Mark' or 'Model' number, denoting the production series of a particular vehicle, just like, for instance, P51C, or Spitfire MkV.
One peculiarity of the German system though, is that it didn't always run in true alphabetical order. It was possible to have, for instance, and Ausf.D before the introduction of the Ausf.A, as happened with the PzKfw V Panther !!!