Board Thread:Wiki Discussion/@comment-5164724-20130415051753/@comment-5532114-20130415230331

Well, they were made to represent VY1 and VY2, while derivatives are characters of their own, usually based on already existing Vocaloid. I don't know why you think they are any different than fanmade Lola design, the only difference there is, is that Roro and Kiku are semi-officially recognized by Yamaha.

So un-official/semi-official designs/avatars would be a term for them.