I think the term spin-off is used to denote an on-going series; the stand-alone episodes and specials aren't so much spin-offs as they are asides.

I especially enjoy the prospect of seeing pokémon documentaries - that would be incredibly interesting, and would finally give people such as myself an opportunity to find out more information about the species of pokémon, rather than just the pokédex entries or the habits of individuals in pokémon battles. We're led to believe that the information for such documentaries exists in the pokémon world through the reports, as well as the very occupations, of the various professors - so to find out what that information is would be intensely interesting.