Hi
I do car imports on behalf and for the little experience i have, if say you import a car manufactured/first registered 2007, March you will pay duty the same as a 2008 Manufactures/First Registered, I don't know why they use that matrix but the following site can give you duty estimates
What I usually do is delay Shipping to arrive at that particular month also note that some various ports in Mombasa have various clearance dates I know KENCONT For SBT has up to 21 days (Confirm with your clearing agent)
Any other Questions I will be glad to respond
http://dutycalc.co.ke/