I am writing an article for a magazine at my school about gene dilution, and I am using the feudal practice of claiming titles based on Salic law as my introduction. Who was the most distant, at least partially successful, known claimant to a inherited feudal title? By partially successful, I mean that his claim was either taken seriously by many, or he was able to start a conflict based on it.
In 2010, David Carnegie, the 14th Earl of Northesk (a Scottish title) died. Despite the efforts of his three daughters to claim the title for the eldest of the three, they were unsuccessful.
Lord Lyon King of Arms (the official who adjudicates on affairs of the Scottish Nobility) confirmed the title on August 13 2010 to Patrick Carnegy, 8th cousin once removed of the deceased 14th Earl.
The new Earl had to trace his descent back 349 years to find the connection which allowed him to inheirit the Earldom as the legitimate male heir.
I don't know if this is the most distant known claimant to an aristocratic title, but it is pretty distant.