Nothing! Ancestry is not complete.
Ancestry does have the complete index images 1837-1983.
Hi Barbara - I have found folks in books written by other family members who are not documented correctly. If you do not have a source given for the information, you cannot assume it is correct - which is the reason for searching the indexes in the first place. Thus said, there are also known to be many errors in the indexes.
My understanding from other postings on RC (being in Australia, I have no first hand knowledge), the local registry offices may find folks who can't be found in the GRO indexes.
Have you found either of the folks on the 1901 census? This may assist to verify their ages.
Trish