The counter only starts ticking once you’ve unlocked the base skin, so far as I know, so if you’ve not done any legion dungeons since getting it, it’s the full 10 ahead of you.
As long as you have the appearance unlocked (which OP says he does) you can still unlock the skins/tints as normal.
OP: Yes, you have to do every dungeon AFTER unlocking the appearance. There isn’t an easy way to track which you’ve already done though (I think - there is an add-on but I recall the dungeon tracking being a bit messy), so I’d suggest doing them all.