It has been seen that there was a special destination of Caithness on the 28th May 1344, to Isabella de Stratherne, who presently became Lady St.Clair of Roslin; that the charter was confirmed 12th May 1362; and that in 1367 the Earldom was subject to a rent charge by reason of the ward of the heir of William St.Clair; and that the Scottish sovereign wrongfully recognised Alexander de la Ard as heir to the Earldom; on whose resignation in 1375 the rights of those in remainder were again ignored. Several similar instances occur in Scottish history, the most striking being that of the Earldom of Buchan and of the Barony of Sinclair, which see. It is not known when Alexander de Ard died, but at his death his aunt Isabella de Stratherne, Lady of Roslin, was next in succession, and we are told by the Diploma that she outlived all her brothers and sisters and their issue, as also her son, Earl Henry I of Orkney, who died 1404, transmitting her claim to Caithness to her grandson, Henry II of Orkney, Earl de jure of Caithness (1420), who does not seem to have secured a recognition of his right, and during the minority of his son William the Earldom was in 1424 a second time granted to the alien House of Stewart, and again in 1450 to that of Crichton. Her great-grandson, William St.Clair, Earl of Orkney, was, however, successful enough to recover it in 1455, when he became 39th Earl, in successional sequence, though first of his house by patent from the Scottish Crown.
NOTE - The Charter of Caithness, if extant, should be examined, to determine the relative seniority of the Roslin and Caithness cadets. It will be observed that the charter of Roslin secures succession first in remainder to William II, Earl of Caithness. Had he been senior to Sir Oliver, the remainder would have gone to the next younger brother. The titles (emoluments) of Carnoch and Innernavir attached to the earldom charter of 1455 refer to estates in the Caithness appanage or province of Strathnaver.