Elwyn, thank you for your comments. Grandfather's cert doesn't appear to be there as all his siblings were named on their birth registrations and also there are no certs for the surname with the correct parents in the correct time frame.
Yes, I was hoping to avoid emailing/contacting the various offices, because Rootschatters often know the answer. Looks like I, or my brother, will have to bite the bullet and make some enquiries when the offices are open again.