That's the official ruling.
My parents were both children at the time of the 1939 register.
My father's 1939 entry (he was born in August 1928) is visible on Ancestry. He died in 2016.
My mother's (born 1929) died 2013 is not. Her sister also died in the same year (though in another country so records won't link) is also not visible.
Interestingly these records were revised over time .
My paternal grandmother's entry has the surname of her second husband written in green (married 1968 )
My 'step' grandmother was single in 1939, became my grandfather's 2nd wife in 1944 and then after his death remarried in 1966. Both these later names and dates are entered in green on the 1939 register.
Possibly my father's entry was opened in error. He also has green annotations (indecipherable to me codes), they are dated 1958 which, I think, is the date he left the Royal Marines Perhaps someone took it to be a death date (??)
His brother is also visible with no annotations and he certainly died in 1976. (no annotations)