Hello Jeff
According to Ancestry family search I was able to find his sister named Gladys Ellen Endacott who married Charles Wilfred Anscombe. This information was confirmed by my mother. So I believe it to be correct. There were several siblings, however, I only heard about Gladys.
Gladys Ellen Endacott was born 17 May 1907 West Ham Essex England.
Married Charles Wilfred Anscombe in Sep 1926 in Tunbridge Wells.
Their parents were: George Henry Endacott & Constance Mary Freeman, who married ih 1897 in Tonbridge Kent.(Ancestry source).
Based on the above information & the fact that the other kin were also born in West Ham, I accepted the 'hint' that Reginald Endacott was born in 1904. However, I cannot confirm any actual birth or death records. Reginald Endacott's year of birth is recorded on the "Anscombe Family" public tree and a couple of others. So I have just gone with that. I feel this is the same Reginald Endacott.
As an aside, I was told by my mother that when her half-brother wrote to Somerset House in 1978 with details of his estranged father, they replied that all the details he'd provided were correct, but that he was never married and had died in 1977. Several years before that during a visit to Cornwall, my uncle was approached by a man in a pub who asked him if his name was Reginald Endacott. It shocked him to the core, and the man told him, that a person who looked just like him lived around the corner. My uncle, did not persue it as he had never known his father and was not emotionally prepared for it.
I hope this helps, and thanks ever so much for your amazing assistance. I am so grateful.
Thanks in anticipation
Best regards
Carol