Dunno. That why I'm bringing it up. All my googling has come up with zero information. A few sources claim it follows the same procedure as boxing, but nothing definitive.
I find it absurd that a champion can come in over weight and still keep his belt. What's stopping a champ from deliberately coming in over weight if they dont fancy their chances against the challenger? They fight at catchweight and he still keeps the belt. Its madness.
Not saying this is the case with GSP. But this area does seem a little murky.