Would I be correct in thinking that the 1841 I.o.M census online on Ancestry.co.uk is incomplete?

I have been searching for Richard CORRIN dob 1794, and wife Elizabeth (STEPHEN) dob1799, which would have given their ages at approx. 47yrs & 42yrs respectively. Their son Richard aged 20 is there, and even though there are (12) Richard CORRINS listed, none of them are the right one. A long time ago I received information that he showed as occupation - Joiner - on this particular census, so now don't know why he doesn't appear on their list.

Any advice appreciated,
Marjery