Board Thread:General Discussion/@comment-67.149.26.192-20150416192408/@comment-88.174.73.204-20150416201732

Miku, Rin, Len and Luka have numbers because they're part of Crypton's " Character Vocal series". Hence the codenames "CV01", "CV02"...

GUMI, who's made by Internet.co, is not part of this series. That's why she has no number. In fact, outside of the Crypton VOCALOIDs I mentioned above, there is no VOCALOID that has a number on their shoulder if I'm not mistaken.