How accurate are most lists of clan septs? I know not everyone with the same surname is related, but I have come across something confusing to me. I am a part of the Urquhart clan. We are a small clan, and the closest thing we have to an actual sept is the name Cromarty. But I recently found out that Cromarty is also listed as a sept of the clan Mackenzie. Can one family belong to more than one clan? I have read that families would change allegiances through the centuries depending on what family was more powerful locally. Is this what happened? Both Urquhart and Mackenzie seem to come from around the Black Isle area.

While I'm asking questions, where can I find reliable sources of information about highland clans in general and maybe about specific clans that are based on actual historical research? I've read about clans from companies trying to sell tartan and clan crests, but I was wondering how accurate this information was.