"The Earl of Ross's March" and another, different piece, "Salute to the Earl of Ross", were allegedly written by Donald Mor MacCrimmon around 1600. That was after Lord Darnley (2nd husband of Mary, Queen of Scots in 1565) had expired with the title in 1567. No matter ... none of the holders of that title was surnamed "Ross", not even the first five O'Beolan Earls nor the Leslies nor the Stewart nor the MacDonalds nor (as noted) Darnley.
It is my belief (after viewing all of the Ross gravestones in the ancient graveyard around St. Duthus Church in Tain) that the Rosses took their name from the land much earlier than was once thought. None of the Earls of Ross (who were O'Beolan descendants) ever had the surname of Ross, even though King Malcolm Canmore (1058-1093) encouraged the use of the duthus/clan names during his reign. King Malcolm IV (1153-1165) appointed Malcolm Macbeth as the first Earl of Ross in 1160. It is difficult to believe that only the "privileged" gentry used surnames during the period between 1160 (or earlier) and 1372, after which the chiefs of Clan Ross began to use the name of Ross as their own surname.
Documents, Illustrative of the History of Scotland, Vol. II, 1286 - 1306, selected and arranged by the Reverend Joseph Stevenson, Edinburgh, 1842, Pp. 143, contain notices of original unprinted documents preserved in the office of the Queen's Remembrancer and Chapter-House, Westminster. There are references in these documents to the "comitum de Ros" in 1295, "le compte de Roos" in 1296, "Willelmus and Robertum de Ros" in 1296 and "Eufemia comitissa de Ross" in 1297. This illustrates the fact that Ross was not yet a surname used by the Earls of Ross.
In The Bruce, or, The book of the most excellent and noble Prince Roberet de Broyss, King of Scots, compiled by Master John Barbour, 1375. Edited by Walter W. Skeat, London, 1894, there is a reference to "The Roß" in the same context as Robert was "the Bruce", and not as a patronymic or surname. It is my contention that the provision for surnames, having existed during the reign of King Malcolm III (1058 - 1093) and following the Norman Conquest of 1066, was not lost amongst the "gentry" during the years leading up to the reign of Robert the Bruce (1306 - 1329). The designation of the Earl of Ross as "The Roß", in fact, infers that there were many Rosses in the Clan which served The Bruce so valiantly. Furthermore, when William O'Beolan (6th Earl of Ross) died in 1372, and his half brother Hugh Ross (1st of Balnagowan) died in 1371, there is evidence that efforts had been in place to groom a line to continue the line of chiefs and to preserve the name of Ross after the loss of the Earldom. Therein lies the impetus for the use of the surname to gain in momentum.