It sounds like EE (and other online shops) were offered solid case packs for Raddus, Sefla, and Galen, which is why they pre-ordered by the figure.
Also sounds like the actual Wave 4 case mix had really, really low numbers. Not sure how many of those made it out, but obviously some did since Robot Kingdom and some other OUS shops were able to get them and sell them earlier this year.
There could still be Wave 4 cases in the distribution chain, guess we play the "wait and see" game like McMetal said.