In 1770 there is another marriage for a Jonathan Gillett, from Family Search:

First name(s) Jonathan
Last name Gillett
Marriage year 1770
Marriage date 1770
Marriage place Chatham, Kent, England
Spouse's first name(s) Elizabeth
Spouse's last name Denway
Residence Chatham, Kent, England
Place Chatham
County Kent
Country England
Record set England Marriages 1538-1973
Category Birth, Marriage, Death & Parish Records
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In 1800 there was this entry on the Death Duty Registers:

First name(s) Jonathan
Last name Gillett
Death year 1800
Residence CHATHAM
County -
Court Rochester Consistory Court
Record set Index to Death Duty Registers 1796-1903
National Archives reference IR27/79
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In July 1800, there was this probate recorded:

First name(s) JONATHAN, SENIOR
Last name GILLETT
Year 1800
Month July
Place Chatham
County Kent
Country England
Court Rochester Consistory Court
Document type Will
Notes -
Source West Kent Probate Index, 1750-1890
Record set Kent Wills & Probate Indexes 1328-1890

and also this:

First name(s) Jonathan, The Elder
Last name Gillett
Status/occupation Shipwright
Year 1800
Year detail proved 1800
Place Brompton Chatham
County Kent
Country England
Court Rochester Consistory Court
Document type Registered will
Document reference DRb/Pwr 39.393
Document 2 type Original will
Document 2 reference DRb/Pw 63
Source West Kent Probate Index, 1434-1857
Record set Kent Wills & Probate Indexes 1328-1890
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His handwritten original will is held with the records of Rochester Consistory Court at Kent Library and Hisgtory centre, Maidstone ME14 1LQ.  It was proved on 11 July 1800 and says he died on 25th of Ult, which would be June 1800.  In it he names:

His wife Elizabeth,
His three sons William, Gabriel and Jonathan.

This will raises one or two problems:

(a) Elsewhere I have a report that his wife Elizabeth died on 5th August 1767, yet she was clearly alive at the time of probate not to mention also at the time of signing the will on 4th April 1791.

(b) Elsewhere I have it recorded that he had a total of six sons, the threeabove plus Thomas, Robert and second Thomas.  It now looks more likely that the last three sons belonged to another family.

NA

Their marriage from Family Search:

Name Jonathan Gillett
Spouse's Name Elizabeth Stedman
Event Date 07 Nov 1756
Event Place St. Mary, Chatham, Kent, England