A record in the Much Haddam Court Roll, dated 18 October 1529, establishes that John Sell died before 18 October 1529, that his wife Joan was living on that date, that he was succeeded by his son John, who was of full age at the time of the court held on 18 October 1529, and that the John Sell who died by 18 October 1529 was the son of an earlier John Sell and his wife Agnes who both died before 31 March 1502. 
Much Hadham Manor Court Rolls. [Ftn: The original, the greater part of which is here translated, is in the Public Record Office. The official reference is "Court Rolls. Portfolio 177. No. 34."]
General Court held there on Monday in the frats of St Luke the Evangelist viz. the 18th day of October 21 Henry VIII.  …
That John Sell 'languens in extremis' and in fear of death out of Court, after the last court by the hands of John Patmere deputy bailiff in the presence of Thos. Patmere & John Migliell surrendered into the hands of the lord one cottage with curtilage called Cranmers in Hadhamstrete parcel of the tenement formerly John Cook's, also one tenement & iij acres of land of 'Molond' formerly John Burle's, also one cottage with one croft of land adjoining next one acre parcel of Schepherde's tenement & the same John was admitted after the death of John Sell his father as before the court with view of frankpledge held there in the 12th & 17th years of Henry VII to the use of John Sell the son & his heirs. To whom the lord granted seisin etc. [In margin: Fine xxd.]
And that the same John Sell who held one tenement with curtilage in Hadhamstret & one acre adjoining called Frebarnes late Clarienc Frebarnes, one homestall of Molond' called Tornerestend with an acre of land lying on the north part except one parcel of land lying on the north part called Hampstall containing in breadth xliij feet formerly John Hunts. To which the same John was admitted after the death of John Sell his father & Agnes his mother as appears in the court held on the Thursday next before Hockeday [2nd Tuesday after Easter] 17 Hen. VII. [Easter was 27 March in 1502, thus the court was held on Thursday, March 31, 1502.] Also 5 acres of land lying in terriesborne in three pieces late Richard Wystard's formerly Simon Colond as appears in court held there as aforesaid & the same John died seised in demesne as of fee & John Sell is son & next heir & of full age upon which came Joan Sell late wife of sd John the father & sought to be admitted as in freebench according to the custom of the manor & she is admitted for term of her life. [In margin: Fine nothing because it appears his wife held in freebench for term of her life.]
John Sell's son John  wrote his will on 9 December 1573 and added a codicil on 23 April 1574. The will indicates that the testator's parents also had a son Simon and a daughter Joan whose married name was Mannynge. 
 "Much Haddam Manor Court Roll," William Brigg, ed., The Herts Genealogist and Antiquary Vol. 3 (1899), 99-103 at 103, [Google Books].
 Janet and Robert Wolfe, Genealogy Page for John Sell, [JRWolfeGenealogy].
 Essex Record Office, D/ABW 34/171, Will of John Sell of Much Hadham, Hertfordshire, yeoman, Archdeaconry records, Commissary of Bishop of London, [Essex Archives].