I want to see if I can answer some of the David Peck issues that have come up. Not that I have the answer(s), but writing might help me consolidate some of my thoughts. However, I don’t quite know where to begin. I think I’ll start with some random questions/comments–in no particular order.
On the David Cook reference. It is in a printed book file. I do not know what the source of the information might be. The text doesn’t give any references. Here is the link to the internet edition and reference to the print version: http://www.schenectadyhistory.org/families/hmgfm/reynolds-2.html
The David Peck document you recently sent to me with an 1839 date on it doesn’t seem to me to be from our David Peck. The DOD is close but not the same. Our DP died 26 July 1839. If our DP had been a Rev War Vet, he should have been mentioned as such in the 1840 Federal Census. I think this document may belong to the David Peck from Rensselaer County. He is listed on the Ancestry.com list and the Agency of Payment is Albany.
On one of the Westchester Co web sites dealing with the Rev War, they had a list of all of the soldiers from Westchester Co. who received a pension. There were only just a few and David Peck was not on the list. From further reading, this is not surprising. The vast majority of the soldiers in the 2nd Regiment (Col. Thomas Thomas) were not regular soldiers but belong to the militia and were responsible mostly for maintaining order at home. They were paid a wage but received no pension. I have put in an interlibrary loan request for the book by Virgil D. White that has abstracts of all Rev War pension files. I’ll let you know what I find when it comes in. A couple of weeks, I imagine.
Which David Peck is which? I get confused and am often not sure who is who, mostly because of the little information that is available. I've drawn out a timeline (1690 - 1850) and entered in David Pecks and approximate marriage dates and try to get a handle on them that way. Where were they and when? Why no wills or deeds or birth/death/marriage records? The David Pecks of North Castle must have had children. What happened to them? Are there some lost Peck children out there for whom we don't have parents? And now I have found reference to another (?) David Peck in the 1840 Fed Census for Blenheim, Schoharie Co., where there are 3 Peck households listed one after the other on the same page. There is David ? Peck (? is perhaps H or N, I’m not sure or either, but there is a middle initial); there is William Peck, and there is Christian Peck (David’s widow). Logically, this David ? Peck should be David Woolsey, but it does not look to me like a W. Can you take a look?
As for the David Peck listed on the four mortgages, I am fairly confident that they are David Peck(1724). Here is my thinking on this. From the North Castle Town Records we know that David1724 was there in 1772 as "overseer of the roads, or all the rest of the roads in the Middle Patent." Others were named overseer of other specific roads. He is also mentioned by Darius Peck as such in his genealogy. And then again from the Town Records of 1775 we hav David Peck as Deputy Constable "to serve as usual." To me, this implies that David Peck had previously served as Deputy Constable and it is very likely that this is also David1724. 
Coming at about this same time are the Mortgages between David Peck in 1772 with Wm Stewart that mentions David’s wife Abigail and the one from 1775 with Shoball Brush that does not mention David’s wife and whom we can then presume is dead. Based on the dates, I believe this David Peck to be David1724. 
The other contender for these two mortgages might be David Peck 1745 who marries Mary Woolsey. However David and Mary Woolsey are producing children in 1772 and 1775 and are still married and living. David 1745 is not married to Abigail as mentioned in the mortgage and is still married to Mary Woolsey in 1775. He is not a widower. Again, I believe these two mortgages are for David 1724.
From Darius Peck we also learn that David Peck "in 1772, resided in what is called Middle Patent, in the eastern part of the town of North Castle, N.Y. near the Connecticut line, and adjoining the town of Poundridge on the east." While I also cannot find David Peck marked on the Map of the Town of North Castle, this does not bother me that much, although it would have been nice to see his name. But I do find the names of Roger Sutherland and Ezekiel Finch , two names mentioned has having land with boundaries with David Peck’s land that he is mortgaging to Shoball Brush is 1775. These properties are located is the area identified by Darius Peck.
Turning to the mortgages from 1784 to John Jay and 1786 to Isaac Webbers, we find that the David Peck of this document has a wife Mary. I believe this is Mary Reynolds, late widow of Jehiel Davis, as mentioned in the Letter of Administration for Jehiel Davis of North Castle, who died intestate. These were issued 1 June 1786. Since it takes some time for the wheels of bureaucracy to churn, I find it perfectly reasonable to assume that David remarried prior to the date of this mortgage. And given that the names in the 1786 mortgage associated with the boundary lines of the property overlap with some of the names found in the previous mortgages, I believe that this land also belongs to the same David. In addition, the witness to the 1786 mortgage is Jonah Reynolds, the brother of David’s wife, Mary.
I do not feel quite as confident about the 1784 mortgage to John Jay because I think this is a different piece of property altogether. It is described as "lying and being situate at Bedford New Purchase." And the names of the property owners surrounding this property are also different from the other three mortgages. But while this parcel is at the Bedford New Purchase and David Peck1745's wife Mary Woolsey came from Bedford, there is no reason to believe that this mortgage not made by David 1724 and that the Mary of the mortgage is not Mary Reynolds. By 1784, David Peck 1745 and Mary Woolsey should be off in either Dutchess or Orange County. David1724 continues to be in a bad financial position, no doubt as a result of the ravages of the War. 
But the mention of David 1745 leads me to other questions I have. In one place I have David1745's son David who married Christian Minthorn as 16 April 1766. I find this date in some of Popenoe’s work, which he says he got from Betty Frasa. Other places, I see David birth listed as about 1770. I also have a marriage date for David and Mary Woolsey as about 1765 with their son David being born in Dutchess County. I have David 1745 moving from Dutchess (if in fact that’s where his children were born, to Orange and then to Delaware County. What do you think? I’m not really confident of my data here.