Sorry I have to open a separate discussion - GOG user here. The mod seems to integrate the new items somewhat oddly into the vanilla tribal factions: They use the Sallet quite frequently, but so far after the first dozen raids not one of them wore a Cuirass.

Unsure why this is - both items seem to be set up identically in the patch file, etc. The vanilla tribals generally wear Tribalwear which does not occupy the Middle layer, so they all have a free slot, whereas the Sallet has to (and does) supplant the War Mask.