Hi Mary. A long message is fine - no one minds, and we are very used to that on rootschat. Many families are very complicated and it takes a lot to explain it all.
In my mind (others will probably have other suggestions which may be better), it might clarify things if you can find the marriage certificate of the
other John then you will find out what
his father's name is.
If he does not give a father's name, then it
might be safe to assume that this John was illegitimate and his mother was Sarah.
Then, putting two and two together, this
could indicate that the baptism you found in 1816 with parents William and Betty, is
your John.
But if this other John names his father as William too (or something else) then you will be back to square one wondering which John belongs to which family.
There may be other John Blundells of course (unbaptised or records lost or not transcribed), but as these two seem to be the only ones whose baptisms can be found, then it is possible that one of them is yours.
Another thing to do is to try to find other children baptised to William and Betty to see if there are any names (such as Stephen) in that family. (As John names one of his children Stephen).
I can imagine what a muddle some trees must be in trying to sort these families out.
