Yep
Cotto fought 3 fights at Middleweight...at a catchweight of 159 when beat Sergio Martinez, catchweight of 158 when he beat Daniel Geale, and catchweight of 155 when he lost to Canelo.
Canelo only fought 2 fights at Middleweight...both at catchweights of 155 (Cotto/Khan)
Just because he can rehydrate doesn't mean that he's "really" anything, he's a Junior Middleweight, because he can still make 155. Once again, is Daniel Geale "really" a Super Middleweight because he rehydrated to Cruiserweight against Cotto? No. You are what you can make. Canelo is a Junior Middleweight who's fighting at 155.
Not true.
Roy Jones Jr won the Heavyweight belt on March 1st, 2003 & didn't drop it until February 20, 2004....almost a full year later.
Canelo won the Middleweight Championship November 21st, 2015 and, as of today, has only held the belt for a little less than 6 months now.