When using the engineering googles from the Create mod that are compatible with both the head and the glasses slots, the cosmetic slot renders them for both. Since you would only want to put the goggles in the cosmetic slot if the head slot needs to be overwritten, it would make sense to only care about that slot.

The engineering googles on the "glasses" slot renders when the helmet slot is occupied, and it overwrites any other glasses items like the monocle from the Things mod.