Not positive about this, but I don't think more than a handful of skins have been rotated out to make room for a higher quality skin. I think the P-51D has quite a log jam of skins in the rotation queue, and many of them have got to be better than some of those in game.
I assume it's a hassle for HTC to rotate skins out and so they rarely do it, but that's unfortunate because this encourages skinners to rush projects to get them submitted, because the skin rotation queue simply doesn't seem to be moving.
Also, I've wondered whether the log files record the skin used, so that HTC can quantify a skin's popularity in game.