I think for the search, it only pulls up titles and the first tag. Someone previously told me this and I did a search of mine for "cat" and it only pulled one with that in the title, but I know I've used that tag other times (thanks to that catbot). ;) The tags stay on the post, but only the first one counts for it appearing in the searches after the 7 days are up. That's my understanding at least. That's why the first tag is super important.