Confirming that the William in 1939 Stillington IS the son of Mary Hannah & Robert, just viewed his GRO birth record. However, I think Mary's yob is 2 years out, ie should be 1873. Last census has her born Hunwick which comes under Auckland reg district.
WOOD, MARY HANNAH HAWKEY
GRO Reference: 1873 M Quarter in AUCKLAND Volume 10A Page 286
SS