The Ellen Birch nee Hart mystery: I even wondered whether she had done a runner or reverted back to maiden name?
Probably too much detail here - but in case of any interest...
The family story that my father (born 1920) knew was that his mother Nell Birch had been brought up by an aunt she didn't much like and got out of Bolton by volunteering towards the end of WWI - and thus meeting and marrying my grandfather - and going off to China with him.
My father was always annoyed (and rather hurt) because she had burnt family photos without discussing it with him - and all in all it seems to suggest she had a not very happy childhood and liked clearing out stuff and memories.
It took me quite a while to track Nell down in the 1911 Census as she is there called Ellen but is indeed living with her childless aunt (by marriage) Margaret Birch and her paternal uncle, Robert Birch, with the last baby sister Ella Margarete (perhaps called after her biological mother Ellen and the woman who became her unofficial mother Margaret).
Older children were with their father (including Frederick). So... all points to death of Ellen Hart - but could that 'Widower' status of John Thomas Birch in 1911 be a polite fiction and she'd gone off with someone else.
But then that seems unlikely with all those children... And John Thomas seems to have been quite a solid sort of figure through his long life: staying in touch with family, leaving a bit in his will.
I had a bit of communication with a hitherto unknown Hart cousin in Australia (DNA matched us), a descendent of Ellen Hart's brother Thomas who went out to Australia. My cousin had a memory of their branch of the family having some correspondence that referred to Ellen's death and the break up of the family but it hasn't come to light.