I'm back reading the early documents and am currently working on a 1638 Gunn document from the Sutherland Estate. It's all highly witnessed and 'according to the acts of Parliament' and so on.
The story In Mark Rugg Gunn (page 140 - 141) that 'Chief' Donald Crottach Gun (around the 1650s) was in big trouble when KIllearnan burnt down as he could be evicted from the land just doesn't ring true; the Sutherland Estate had at least a copy of the Killearnan and Navidale 'charters' as Gunn did not own the land but 'rented / leased' it. I suspect the original 'charters' were held by the Sutherland Estate; why would a person renting / leasing property be given the original? The Sutherland Estate worked on a legal, fully documented basis as shown by its archives.
The Crottach tale is all part of the traditional Gunn mythic history view that Caithness and Sutherland were virtually lawless which they certainly were not. Gunn coroner, in the mid 1400s, was part of the legal / judicial system of the time even then. That's two hundred years before the Donald Gunn Crottach doubtful story! The Sutherland Estate was a huge, wealthy enterprise whose owners were of national importance; to suggest such an Estate would be involved with legally doubtful events is very questionable.