Just Be Friends in English was only done for Miku Expo 2014 LA and NY (four shows in two weekends) as far as I know. Mikunopolis before it used the Japanese version. It might have been a one-time license since the lyrics were licensed from another creator.
Ah, I see. Yeah that makes sense. I was actually a little worried that global/US success would have them translating more of the songs, but if it requires a bit of untangling rights, I guess it's unlikely to become a problem.
That said I do think new English Miku songs sound a great deal more natural than previously, I just would hate to go to one of these things eventually and they play a jerky, awkward English version of an older Japanese song I love.