Hello

It is best to purchase the 1936 marriage certificate to be certain that you are tracing the correct family. This should give you more information, such as Father's name and occupationm and possibly an address.
If you are correct about the dob there is only 1 possibility on freebmd:
Griffith Jones with Mother's maiden name Jacob in 1916 (Sep quarter)
Pontypridd volume 11a page 1036
The birth certificate would provide more information, however there is a possible marriage in 1915 (Dec quarter):
Griffith Jones and Elizabeth G Jacob
Pontypridd volume 11a page 1333
Kind Regards
Morgan