Success in another division does in fact carry over. For example, Frankie Edgar got a titleshot for his featherweight debut after losing his belt to Ben Henderson at lightweight. He didn't have to start from scratch at Featherweight and work his way into contention, he got a titleshot based on his accomplishment at LW. Didn't hear anybody saying Edgar needs to prove himself at FW before he gets a shot at Aldo and rightly so. Because Edgar has proven himself to be a top LW. Cormier did the same, he was arguably the #2 HW in the world before dropping to LHW. Cormier also dominated one of the greatest fighters of all time (Hendo). Back then, if GSP decided he wanted to move up and fight Anderson for the belt, nobody would be claiming he needs to start from scratch at MW and earn a title shot or say his accomplishments at WW mean nothing at MW. If Anderson wanted to fight Jon Jones for the belt back then, nobody would have said he needed to earn a title shot at LHW and his accomplishments at MW mean nothing at LHW. If Jose Aldo moves up to LW to fight Anthony Pettis, nobody will say Jose Aldo needs to start from scratch an earn a title shot because his accomplishments at FW mean nothing at LW. If Jon Jones decides he wants to move up to HW and fight Cain for the belt, nobody will say he needs to start from scratch and work his way up to a titleshot because his accomplishments at LHW mean nothing at HW. You get the idea. A fighters accomplishments from previous weight classes can be taken into account for that fighters new weight class.