
You must be referring to "Hubert de Burgh: A study in constancy
by Clarence Ellis" (p. 185):
https://archive.org/details/hubertdeburghstu0000clar/page/185/mode/1up
Seems like a valid source to me, certainly better than none at all; I see no harm in correcting his birth and death dates in accordance with the source.
Some additional sources are listed with this Wikipedia article.
https://en.wikipedia.org/wiki/Hubert_de_Burgh,_Earl_of_Kent#CITEREF...
I went ahead and corrected the dates, he's my 22nd ggrandfather and I see no reason not to fix it since we have a good source.
Hi Debra
"Hubert de Burgh: A study in constancy by Clarence Ellis" is the only full--length academic biography of Hubert de Burgh, and it's extremely useful for other members of is family as well. The Oxford Dictionary of National Biography has a short,, but accurate, biography of Hubert, but sadly not one of John de Burgh.
Best regards
Stephen