I envy you having such old photos of your ancestors !

How do you know for a fact your William was born in 1779 yet you don't have the PRs as far as I recall. Please be advised the dates quoted on Census Returns are very often vague estimates and not exact at all, they were merely what the people believed, or wanted to believe, at the time the census was taken. These dates etc were not subsequently checked against any other database.
This site gives an excellent insight how to interprete the various BMD records, it shows why a person's age is often inaccurate, indeed in some census's the ages were all deliberately rounded up !.

http://www.dixons.clara.co.uk/Certificates/indexbd.htm

I hope this helps, sorry if I'm stating what you already know.