Hi Macbaryn,
First a general note you may find interesting or useful. Medieval research I've been doing lately has taught me a few lessons about Earls (of wherever) and their numbers. Earldoms were 'created' and you might get several, numbered 1 - whatever, then the Earldom would lapse. It would often then be recreated at a later date, known as the 2nd Creation, and then the numbering system started again at No. 1 and so on. I've come across numerous Earls with the same number generations apart, all of different Creations.
It would seem (from 'google') that in 1759 the Fife title was recreated and was bestowed upon WILLIAM DUFF.
"In 1759, William Duff, who had served as Member of Parliament for Banff and become Lord Braco of Kilbride, was created Viscount MacDuff and Earl of Fife. A wealthy man, it was he who commissioned the building of the magnificent Duff House in Banffshire".
Duff house is now an hotel but remained in the hands of the Duffs, Dukes of Fife, until 1906:
http://www.bestloved.com/attractions/duff-house-in-banff-scotland-uk.phpHope this helps a little.
Jill