There hasn't been any Kentmere matt paper, at least in FB, for a few years now, they never made a true matt paper, but when they were taken over by Harman all FB matt stopped, they are not, as far as I know, stopping the fine lustre in RC vc select, but the only kentmere FB paper currently in production is the Fineprint glossy, so if you have been using any Kentmere fb matt paper it must be very old stock, as an aside, Ilford still make a true matt paper in both RC (The silk, I think) and the FB papers.
Richard