Taking another look at James' death certificate it does appear that Mary was still very much alive as she was the informant and present at the time.
You didn't tell us that in your opening post. Does the 1921 death cert definitely show her as wife/widow?
If it does then it makes the 1925 marriage possible. Have just found a Mary A Henton
living in the Epsom RD in 1911. Checking her back to 1901 she hasn't aged!! Nor has her husband. I think the 1913 death is hers and not Mary Ann Hinton
1901 aged 43 born Sutton Surrey
1911 43 born Sutton Surrey
1901
Edward Henton 44 b Horsham
Mary A 43 b Sutton
Thomas Kenyon 5
John Duthie 44
Frederick Cartwright 58
RG13 Piece 580 Folio 72 Page 11
EDIT
Just to demonstrate the difference one letter can make. Edward HENTON married Mary Ann HILTON😳