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Looking at Parish Records on F M P there is a burial record for Thomas Jocelyn age 24 on 20 Oct 1891 at Little Hadham which would fit with the Thomas Josling/Joscelyn despite the death being registered in the Hertford Reg District
In the GRO Birth Index Joseph Thomas
GJosling's birth shows no mother's maiden name so presumably his mother was unmarried and sadly I can't see any baptism records for Joseph Joslin or Joseph Thomas Josling with variations of the surname.
Working on the basis of the 1911 census being a good possiblity with a birth place as Little Hadham the only Joslin/Jocelyn family that I can see in Little Hadham is below in 1871 living in Little Hadham and mistranscribed as Goslin
Joseph Goslin 60 Blacksmith Journeyman b Little Hallingbury Essex
Sarah Goslin 52 b Matching Essex
Isabella P Goslin 5 Granddaughter b Little Hadham
Charles Goslin 16 Son b Braughing Hertfordshire
The granddaughter Isabella was baptised in Little Hadham on 5 May 1865 as Isabella Phoebe Jocelyn with mother Emily
I think this is the family in 1851 living at Thorley Street Cottages, Thorley Street, Thorley, Bishops Stortford although the surname is so badly written it was a miracle it is transcribed as Joselyn
Joseph Jocelyn 40 Black smith Essex
Sarah Jocelyn 32 Essex
Emily Jocelyn 11 Essex
Joseph Jocelyn 7 Essex
Frederick Jocelyn 3 Hertfordshire
Francis John Jocelyn 0 Thorley, Hertfordshire
I can't see Emily post this census but given Isabella's birth was registered, she was baptised and looked after by her grandparents it looks unlikely that a second illegimate child would not have had similar treatment

Apologies that this doesn't take you any further forward but I will continue to fiddle. There is always the possibilty of a name change. He might have been registered under his mother's surname and it may be useful to look at other Josephs born in the Sept and Dec Qtrs 1868 in Bishops Stortford Reg District. I noticed a Joseph Hale who was registered in the Dec Qtr 1868
JOSEPH HALE mother's maiden name SMITH GRO Ref 1868 Dec Qrtr BISHOP STORTFORD UNION Volume 03A Page 256
and a baptism on 27 Sep 1868 at Little Hadham with parents John and Eliz and I can't see him post 1881

Kay