I have built my own database of Clans and their Septs. So far 4,000+ names and counting.

You are quite right that Swan is counted as being both Gunn and MaQueen. I would point out though, that Sveinsson, Svenson, Swan, Swann, Swanney, Swanson and Swenson are all Gunn. A ratio of 8 to 1 in favour of Gunn.

As a general rule of thumb, surnames come from one of four categories: place name, physical characteristic, trade or son of name. I would argue that Swan is a corruption of Swen and is a Norse (Highlands and Islands) name,

Or,

Is a Gaelic trade name. If it is a trade name in Gaelic then it is more than likely that it could occur in more than one clan (every clan needed metalwork done, so there would be a Gow in every clan).

There is as well the whole concept of Sept to be considered. Some were little more than slaves (tied to the Chief); some had more independence and farmed the clan lands (they could leave, but the land stayed behind); some had even more and were paid employees. I believe that the Lamonts hired the Von Alroths (German stonemasons) to build them a castle. The whole process lasted 150 years and the Von Alroths became a sept of Lamont.

So it is possible that your forebears were jobbing workers, moving round the highlands from one employment to another and if and when they settled became a part of the clan they were with.

I am not going to say "Pick one", but I will say, be aware that you might never find an answer.

Regards and good luck

Chas