[CentOS] An R rpm question

I've had a request to downgrade R on one server, to match three others
(someone who's just left had important scripts, and I assume they break
going a full subrelease...). The server they want downgraded is running
4.1.0-5; the others are running 3.0.1-1. ALL are CentOS 6.5, yet yum
downgrade tells me "only upgrade available", and yum list R-core-3.0.2\*
gives me "no matching packages".

Anyone know what's wrong here?

        mark