There is a marriage in the June quarter 1930 in West Bromwich of a Samuel Davies and Dorothy Phillips:
Marriages Jun 1930
Davies Samuel Phillips W. Bromwich 6b 1979
Phillips Dorothy Davies W.Bromwich 6b 1979
It is possible they married after the birth of Dennis. Have you purchased this marriage certificate? Is this where you saw their ages as "full"?
Yes I have that marriage certificate but I can't prove if its him or not, there is nothing conclusive one way or another. I don't believe its him tho.
Regarding the full ages comment I made, please disregard it, I actually don't have any certificates that mention their ages as being "full", must have got muddled up.
I could post a picture of the certificate, are we allowed to do that?
You would probably need to do a bit more digging to see if there are more couples with the same names marrying in a similar time frame, but if your grandfather's parents are named as Samuel Davies and Dorothy Phillips on his birth certificate, I would have thought this marriage has a reasonable chance of being the right one?
Dorothy is not a hugely common name, and especially considering her surname and the husband's name being correct, it looks promising.
What are the ages of this Dorothy and Samuel when they married in 1930?
What leads you to think it is the wrong marriage?