The posts are so numerous that we need an index. Probably several thousand posts ago, this issue was discussed at length. It was shown that contemporaneous newspapers and other things referred to the Republic of Kenya in 1963—in advance of the 1964 official name change. A poster put up an image of a newspaper article from 1963, showing Republic of Kenya in the actual article.
Amen to that, but I was just answering Neighbor's question. Whatever the birth registry forms said in February of 1964, I presume that post-1964 forms say "Republic of Kenya." If the document is a forgery, something as simple as the availability of such a post-1964 form to the forger might explain its use. That all applies ONLY IF the posted document is a forgery, which it might not be.