The mat converter takes the key passed in from whoever is calling it. It doesn't make its own names. If you already asked for the key before, it returns the existing material it wrote before, even if it was not the same material. If you pass a different key, even for the same material, it creates a new copy.

I'm still at work so cannot look at the script. Printing self.mat_key tells us nothing because maybe it isn't used. Certainly the material is not called Victoria 4. It must be concatenated with the material name. If it is just passing the material name, then that is why you do not get separated materials for the two figures. You have to check if the call to the mat converter is actually receiving the concatenated name.

[Edit] Cross-posted with your last post adp. I'll look at it later.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)