Len,
Do you have details that confirm that the Henry m. Sarah 1874 Liverpool (Sarah James or Hiorns in the IGI??) is the son of Samuel Corkish & Ann Quayle?

My theory is if John Henry b. 1865 mother died before the 1871 census, that would probably explain why he is living with his grandmother if his father Henry is away working or at sea.

If so, John Henry's mother would have died between 1865 & 1871, a burial that might fit as wife of Henry Corkish and mother of John Henry is:
CORKISH, Elizabeth 33 Bri 4 Sep 1869
This is from the Burials list on IOMFHS website,
I can't find this record on IGI though.

What do you think?

Regards
Kim