According to Nick Howell, there was a lot of speculation about his true birth date as he did not tell the truth on this until some records were found after his death.

Nick Howell claims that she was born in 1913. He’s likely to know, and I’m not sure where I got my specific date from. A daughter, Tess, who died. (According to a comment on a scrap of paper in Pop’s handwriting, found after his death.)