They actually decalred themselves a Republic in December of 1964. The issue would be whether they knew that was coming and created the Republic of Kenya stamps/titles/etc. beforehand.
I would say judging by these references they did.
There should be many people born that year with the same type of BC, one would think. How does this compare?
It became independent on Oct. 17, 1963 via an agreement between Prime Minister of Kenya Messrs Jomo Kenyatta, and the Prime Minister of Zanzibar M. Shamte nearly TWO months earlier than the rest of Kenya declared independence on Dec. 12, 1963. The Muslims in the ten-mile strip, called themselves the "Republic of Kenya" in 1963, before the rest of the country was officially known by the same name on Dec. 12, 1964: