The only way to ascertain which, if any clan one's ancestors' were associated with is through genealogical research, either through the paper trail or perhaps Y DNA testing.

Many of the clan associations as well a tartan merchants have all sorts of bogus lists of alleged septs. Most are Victorian era inventions. The Gunn clan is probably one of the worst offenders. They list surname as septs many of which are not even of Scottish families. If you are interested, there are a couple of threads here on X Marks presenting both genetic as well as demographic evidence of this clan association's misleading claims about its septs.