> All of this said I think most of what you are talking about is
> educational material where YOU CAN'T FIND the rights holder after
> a serious effort.
Even for educational materials it's just as complicated in my opinion. I
don't have a specific example at hand but it's just as true that for many
educational productions, various aspects (music, stock clips, stock
illustrations, etc.) are licensed from 2nd parties.
Educational materials' purchases are basically usage 'licenses' like any
other media licensing.