I noticed that quite a number of CG idols are listed under this category, which at this point in time makes no sense to have them filed under there, or for the category to exist. It may have made sense in 2011/2012 when CG debuted and you could classify them as unofficial due to being outside the main series, but nowadays, after CG has exploded in popularity, it doesn't make much sense to have them there. Especially since they have a more fitting category "Cinderella Girls idols" to themselves. I think that we should remove all the CG idols from that category and place them all under "Cinderella Girls idols" if they haven't already.
As for what Unofficial Idols means, I was discussing this with somebody else from these forums that perhaps it can be changed to "Minor Idols" as in idols that only make minor/singular appearances such as Shinkan Shoujou, Devil Angel, or Yumeko Sakurai, since "unofficial" is too vague of a term.