That I don't know. There were old provinces - like NFD. Kericho for example was in Nyanza. The old province was not tribal. The British had almost haphazardly split Kenya.
In 1962 - The British hired a Prof of a surveyor from the UK to demarcate Kenya into provinces and districts - folks were unhappy with old provinces and districts.
That commission went around asking Kenyans where they wanted. Naturally, Kenyans wanted to remain with their tribes. Kipsigis for example wanted to get out of Nyanza and join fellow Kalenjin.
In the end - 1962 came up with 8 provinces - and 43-45 districts (Bomet and Nyamira were added by Moi - I think Homabaya or Nyandaraua were covered by Kenyatta-Jaramogi). It also came up with 8 provinces.
This was largely a fair process - tribal demarcation if you will - at the district level.
In 1966 - Kenyatta and Jaramogi - connive to alter boundaries. Nyandarua was carved from Nakuru and taken to central. Kirinyanga was carved out of Embu and Eastern and taken to Central. Jaramogi or Mboya got Kisumu split to Homabay.
In the early 1990s - Moi also started. He split Kisii into Nyamir and Kericho into Bomet. Giving us the current 47 counties
And then avalanche started. All which were declared illegal later because I think they didn't follow the law.
You fail yo state one way of containing mt kenya was co.ing up with provinces. Mt Kenya people were scattered all over and substantial number were in eastern and Rv. Actually do you know the representative of Central came from Embu ? Nyaga that tells uou alot