The inventory note does not date the charter in question.
However, the grant, if the report is accurate, must have taken place after 1231, the date of the death of Earl John, last of the previous lines of earls of Orkney and Caithness.
Although the name of the witness is given only in abbreviated form, the reference to the county of Angus suggests that it must be Malcolm Earl of Angus who is shown above.
The separate primary source references to an individual named Magnus indicate that this suggestion is probably incorrect.
From a chronological point of view, Magnuss estimated birth date range as shown above suggests that he was either the son of Gillbride Earl of Angus by a second marriage or that he was the son of Earl Gilchrist.
A more sensible suggestion is that, assuming Magnuss right to Caithness was inherited from his mother, she was related to the last Earl John, who died in 1232, and whose rights would have been divided between his two heiresses.] .
Balfour Pauls Scots Peerage states that William King of Scotland granted lands of "Purin, Ogguluin and Kinminethen" [Powrie, Ogilvie and Kilmundie] all in Forfarshire to "Gilbert son of the Earl of Angus" by charter dated to [1172/77], and that "from him are descended the Ogilvies of that Ilk, Airlie with its cadets, and Inverquharity" ([1175/85]-1239).