so their talk about getting rid of 'Mechs associated with the IS Clans was probably just that, all talk...
probably started with the likes of the Ice Ferret, then when they could only replace it with the Viper (another Mech associated with an IC Clan), they just got pragmatic about it and said "whatever"
after re-reading WoR:Supplemental, it seems to me more like the Mechs they couldn't make anymore in the Homeworlds, they said "bah, IS taint!" and wrote them off