Sorry to come late to this party. I have been chasing George & William Fiennes-Clinton for a little while & in doing so have come across this lineage. The only offered proof of which, seems to be Dalton's Army lists & a coat of arms.
The William mentioned in the army lists, I believe, is a son of Francis & Priscilla Fiennes-Clinton (Francis = son of Sir Edward Fiennes-Clinton & grandson of Henry, the 2nd Earl of Lincoln. And also, he was father to Francis, the 6th Earl of Lincoln.)
George (bap:1636 St Lukes, Chelsea) & William (bap:1638 Threekingham, Lincs.) have been amalgamated by Dalton in his army lists. But George was the Major mentioned; as Helen Ford has shown in her answer; & he can be found a few times in the Calendar of state papers etc.(example: https://archive.org/details/cu31924091770473/page/n181)
The brothers were sent to Tangier & George was killed in an ambush whilst leading a sally against the Moors on 3rd May 1662 - this has been misattributed to William (because of Dalton's mistake) & also to Nathaniel Fiennes (I don't know why) but I think George should finally be given his due.
(George also knocked about with a Major Killigrew, & they were both, at one time, under surveillance by Downing as possible anti-royalist agitators. But I haven't been able to ascertain yet if there is a link between this Killigrew & the family the 6th Earl of Lincoln married into.)
As you can see from the army commissions, William seems to still be around after 1662. When peace was signed in Tangier in 1666, the regiment he was in was sent back to England.
The problems with this lineage:
1. I don't believe Charles Clinton claimed to be a grandson of the Earl of Lincoln; this claim seems to have come after his lifetime.
2: William, the soldier in Dalton's, is not the son of Sir Henry Fynes of Kirkstead.
2. William, the alleged grandfather of Charles Clinton, was supposedly a Royalist officer, but George & William were in a (former) Parliamentary troop. (I can find no details of a Royalist officer with his name - Fiennes or Clinton.) William was supposedly in France, then Spain, & then Scotland - this does not fit the movements of this William Fiennes-Clinton. (The troops in Dunkirk were made up of former commonwealth soldiers & a couple of Irish catholic regiments. Which is always a good mix; as you can imagine!)
3. William Clinton's son James was apparently a politician & soldier - I cannot find any details of either of his careers - he also went to London to get his lands back & was refused (or was successful, depending on the account.) Where is the evidence of this? Suits? Petitions? Has anyone found any?
4. Gov. George (Fiennes)Clinton (Gov. of New York from 1741) - The William & George mentioned in the army lists would have been uncles to Gov. George (Fiennes)Clinton. Apparently, Gov. Fiennes-Clinton recognised the 'distant' relationship between himself & Charles Clinton (I have only seen a letter where he mentions 'Mr Clinton'. I don't know if anyone has found any proof of this assertion.) But Charles's father would have been George Clinton's cousin - so not so distant. (Also, there is the story that Charles Clinton named his son George after the Governor; but they didn't meet until 9 years after his son George was born.)
5. The coat of arms - it was said that Charles Clinton & Gov George Fiennes-Clinton bore identical coats of arms - I would be surprised at this, as George Fiennes-Clinton's arms had a crescent for difference (as is usual.) The chances of them being identical should be minimal. The only example of the Charles Clinton Arms I could find was the seal of his son George & it is not a good image.
https://archive.org/details/civicancestryofn00wild/page/n89
The arms bring me to the Clinton family of Ulster. The Irish Clinton family were VERY distantly related to the family that became the Earls of Lincoln; some members of the family apparently went to Ireland in the 12th century & crucially they bore similar arms. The Irish Clintons had most of their lands taken away after the rebellion (1641) & one of their number, Thomas (I think), was able to recover some of these lands after the restoration. (Could this be the story that morphed into James Clinton going to London?)
There are so many questions unanswered - like why would William drop the name Fiennes when he was obviously using it previously? Why wouldn't any of the English family know of his whereabouts & family? (He was close enough to leave all he had to his sister a few years earlier.)
I do wonder if it hadn't been for the proximity of Governor George Clinton (Fiennes), would Charles Clinton have a different family tree? I think the Clinton lineage needs a bit of detective work. It seems to be have been accepted with little or no evidence.
Anyone interested in the Irish Clintons should look at these 2 documents (On Jstor - it's free to register & look at 6 documents a month.)
https://www.jstor.org/stable/27727928 - The Clinton family of Louth. (This has an example of one members coat of arms & mentions another, which is remarkably similar to those of the Earls of Lincoln.)
https://www.jstor.org/stable/27728747 - Clinton Records.
My search for William (of the army lists) continues, it may turn out he did go to Ireland, but I am doubtful.
https
