Hi, many thanks to you all for your input, it seems to be more common than I thought.
Lisajj, yes they are apart, he was on the "Home Trade" vessels, coasters etc, the other side of the census form for the ships crew does give the skipper the opportunity to state who was not on board the vessel and he states 2 members were ashore and therefore do not appear on the census return.
I now assume that his wife was the person who made the error.
Frank