I'm not sure if being historically correct is the goal to achieve (for sure, for historians it is). Think about the first Robin Hood or knights movies, being a success and I don't assume that the knights on those days had always been that "handsome" and clean, Robin Hood has been wondering around in pair of tights and the castles had been that bright and tidied at the inside as shown. I also do not think that armors had been that bright and shiny in the past, even the "silver" ones (which I assume wasn't not made from noble metal but simple iron or metal).
I think, Kevin Costerner's Robin Hood also wanted to be more "historically correct" (w.r.t. the time it's playing in) in contrast to the classical Robin Hood movie plays but they had added several elements and designs which just looks cool but for sure are not historically correct. So I think it's more a matter of what looks cool (acording to the current taste of "coolness"). And I think that's how the process of design is working. Is there anything said, how those 20 outfits initially are found? If those would have been choosen historically correct there wouldn't be an issue with the process after all
I wonder why being that historically correct if keeping in mind that PM is a toy for fun and the figures just should look like somehow the period of time belonging to.
I think there has been a similiar discussion around about the eye patch of pirates if I remember correctly ...