True- so for, say, a Loup-Garou with the Catch "Inherited silver weapons" and Mythic Recovery, I'd have "Arm cut off" as a Severe consequence, and "Arm cut off with an inherited silver weapon" as an Extreme consequence. I think Extreme consequences are extreme enough to justify that.
To be clear- I wouldn't be downgrading normal consequences because "this guy heals fast, so they matter less," as that devalues the healing power; Extreme ones are already an exception to several of the standard rules, as they modify an existing Aspect- thereby changing the core of the character- so I think they deserve special treatment.