And since they knew they would be a republic, they ordered blank forms with that on them.
Nice theory, now all we need is an example of a Government document with a Republic of Kenya letterhead during the Dec 1963-Dec 1964 Dominion interregnum.
If this were some document we didn't like, we'd cry forgery over this one point. Until this is cleared up, we should treat this document with that wary suspicion that greets wet dogs.
Anyway, for birth certificates back then, it is possible they just came on pads from a printer and were torn off when needed, filled in and filed.