It would not appear if that tag didn't exist. Anyway, if you can't add a tag that you want in your question, post it anyway and someone (probably me) will add it for you.
- Edit: By the way, I also remember Pokemaster saying something about the Tag system not showing suggestions properly so also keep that in mind.
-Sam Sam Sam Sam
4Sam covered it all perfectly. There wouldn't be a tag showing up that didn't exist. It takes 500 points on the pokebase to add a tag. Like 4Sam said, an editor, expert, or mod would add in the tag if you posted in a comment that you wanted to make a tag. Just remember that the amount of points needed, 500, is a bit high for a reason. Its because if some low ranked user kept making stupid tags then it takes out time of the editor's, experts, and mods day to delete the tag and that user would probably get banned.