I'm a MacDonald of Clanranald, but had I never met my father at nineteen years old (me not he) I would never have known this and likely worn Clan Donald or MacDonald of the Isles. Within Clan Donald many clans were born and some absorbed back into their parent clan. Many MacDonalds of Ardnamurchan were folded back into Clanranald as I understand it. If I discovered that such was the case for my line I might consider adding such a tartan to my wardrobe. My step-father, the man who raised me, is Clan Anderson and I may just do that for his tartan anyhow. Perhaps some Swans in your past were too far afield from the Chief Swan of Swan and allied themselves with Gunn. perhaps others did the same with MacQueen.

Long story short;

If your trail is now cold, you should follow your gut and/or go with the broad brush stroke of using the Swan/Ramsay tartan. If, at any time in the future, your digging yields new results, well then you're within your rights to switch loyalties. It's normal practice.