Non-workshop add-ons don't show up on dedicated server.

I was making a new sandbox dedicated server a while ago and came across a very strange problem. Normally, to put add-ons into my dedicated server (if they are workshop) I’ll download them in gmod, put them in gmadconvert.exe, then extract the contents of the folder (except for the addon.txt) in my C:\SRCDS\orangebox\garrysmod folder and they work. I do the same for non-workshop mods just not putting them through gmadconvert.exe, obviously. Now, for some reason, only mods that I actually tell the server to download with workshop.vdf work. The problem with that is, is that not all the mods I want are on the workshop. Does anyone know why this could be happening. And yes, all the mods I’ve tried using are updated for Garry’s Mod 13.