Any bowling historians know what the difference was between these coverstocks from Columbia balls of the mid-late 90's? Tour Boss line had Super Flex II and the Messengers had Super Flex I believe. Thanks!

Super Flex II was likely just a stronger version of the original.  Think of it like PowerKoil 17 and 18.  A modern take is Storms Reactor covers as there are multiple versions with increased strength as you move up (Reactor, R2S, R3S, etc).