Yes Kirinyanga was part of Eastern - Embu district. Kenyatta Jomo in 1960s in bid to shore up Central numbers moved/carved out it out of Eastern - saying they were more kikuyus than Embus. In reality there were few kikuyus in Kirinyanga near Sagana - while rest were Embus like my wife. The names, their dialect, and etc are closer to Embu than Kikuyus. Kikuyu Karinga never regard them as Kikuyu proper (Muranga-Kiambu-Nyeri)
Infact there is really no border btw Kirinyanga and Embu - Kirinyanga county goes to Embu town - border at town - people live in either side - it very fluid - moving btw kirinyanga and embu - settling is no biggie - and so is communication issues - they are almost one tribe.
Kenyatta also moved Nyandarua from Rift Valley to Central.
Yes my wife things Gichugus, ndias, are more tharakas than Okuyus. You pick them for running mate at your own peril. You want the real deal pick mainstream Okuyu and you are shoe in.