If you're wanting more on John Watson, then as well as hunting down his death registration I'd strongly recommend looking at the birth registration for William. To expand on what I wrote above, an 1855 birth registration should include (not necessarily in this order):
Child's name; sex; date, time and place of birth; baptismal name (if different) or name given other than at baptism
Father's name; rank, profession or occupation; age and birthplace; when and where married; any previous issue, both living and deceased
Mother's name and maiden name; how many children she has had; age and birthplace
Signature and qualification of informant, and residence if not where the birth occurred; whether they were present at the birth
OK, you can get some of that from the 1851 census, but there are important bits that you can't.
