I tried to search for contacts that had both of two tags using the "add another" feature of the advanced search, but it was clear that many of the resulting contacts did not have both tags. Also, one tag has 9222 contacts and the other has 2704 contacts but the search returned 9437 contacts, which means that it is mathematically impossible that the search that I intended to make was successful. The results should have been narrowed down, not expanded.