Title pretty much says it all. I downloaded some clothing, hair and jewelry (crowns/tiaras) from various sites like this one and medieval sims, but only the clothing shows up in CAS. Clothing works just fine, but the hair and jewelry aren't available. Like I never installed them. The package files, however, are clearly in the downloads folder. Am I missing a step for hair/jewelry meshes? I have every mesh installed. Every necessary package file is present. Where am I going wrong?

Have you looked under accessories for the jewelry? People have been making jewelry for sims since before Bon Voyage made it a thing, and they made it as accessories. Even a lot of new jewelry is still made that way.

For the hair, alas, I have no suggestion. Unless maybe you've got it subfoldered too deep and the file names got too long? But that shouldn't affect just these most recent files. Have you downloaded hair before, that does show up?

This may sound obvious, but have you checked under the 'custom' tab for hairs? Some creators don't 'bin' the hairs they make, that is to say, they don't make the hairs so that black shows up under black and red shows up under red.

If it's crowns and tiaras, they're probably in accessories. Also remember that for most CAS items, the mesh and recolors are separate, so you need both for them to work. If you only have the mesh files, they won't show up ingame.

Depending on the jewelry, it could be the items are only accessible via the jewelry stands.