Help needed re invisible meshes on beast race

[Because]

Hi there relatively new to modding and I'm trying to add a mesh for a mask so that it shows up on beast races.

It works fine for default races and I've set up the Nif files and armor addons for the beast versions, but I can't get them to appear in game.

The armor addons were copied from vanila items that had .Kha & .Arg entries and the meshes show up the biped model viewer and I've got the correct races selected.

The only difference is that rather than the standard circlet slot I've used slot 44 (the empty Mod slot for mouth/face) which I've matched on the Nif Files

I've looked through lots of guides and searched for an answer to no avail so wondered if anyone here could tell me what I'm doing wrong.

Thank you.

[Because]

Ok found answer (on a distinctly NSFW page on LoversLab) and thought I'd post the answer here in the hopes it would be easier for other people to find.

Once you've created the appropriate armor addons you need to add the additional models to the armour in question. It's hidden on all of the standard ones (unless you click show all) which was why I didn't see it when I copied them.

Hope this helps someone else.