Whatever works for you. BT doesn't have hard rules for stuff like this, hell, it barely has guidelines. Do you want a Bruin for the Wolves? The Wolves could've traded some from Ghost Bears, but not in large numbers enough to show up in MUL.
If you do need a rule, then my rule would be: Fluff text first (since there are cases when MUL and fluff are in conflict), MUL secondary, RATs tertiary.
RATs are meant for quick force generation, and are something of snapshots what may be available right then, but they aren't really indicative of what's common among faction and doesn't tell anything about how common things truly are.
EDIT Swapped MUL/fluff order for more logical one.