I've noticed that currently, some of the eye collectibles are in categories which in turn makes them exclusive to items in the same category. And on top of that, they're not even all in the same category! An example is the Oracle Eyes, which are in the "facial hair" category, meaning you can't have oracle eyes and a beard at the same time. The Spiderkith eyes are in the head marking category and so, you can't mix and match them with any of the other face marking. It looks like we'll be getting a new eye collectible in the upcoming crown crates. It would be nice if they added a new category specifically for these eye modifiers so that we have a bit more flexibility.