Can anyone please explain this to me:

If I download a mod that changes an NPC's face, and there's a neck gap issue, I do what the modder recommend and use setnpcweight. The neck gap will disappear together with any warpaint. I save the game and restart Skyrim. Warpaint is back, neck gap is still gone.

But when I change an NPC's face myself in the CK something else happens (and yes, I remembered to export FaceGenData). I see a neck gap, I use setnpcweight (using the weight set in the CK), the neckgap is gone together with the warpaint. I save the game, I restart Skyrim, the warpaint is back - but so is the neck gap!

I spent far too much time searching around to try to find out why and how to solve this, and I don't understand in what way my own mod differs from the ones I've downloaded - no custom races, no custom hair, nothing like that. There obviously must be a solution, or there wouldn't be any working face replacers for NPCs out there. So please. Help appreciated.

Nevermind, I figured it out. I had based the character's appearance on a character I had made myself and saved a preset for. What I forgot what that the preset had a different weight than the original NPC. It's all sorted out now, this can be closed.

Closed at OP's request.