You can transfer the license to your name, I think, when buying from someone but Graphisoft charge a pretty penny for that.
As far as I know resellers only sell new licenses not old ones.
Can't answer your question because I have no idea, but ArchiCAD wiki has provided a great list of all the ArchiCAD releases (including their features) over the years - http://archicadwiki.com/ArchiCAD%20versions