I mean, at least in Platinum. I read in my Platinum guide, as well as having experience with this myself. Ya know, we can solve this problem easily with the Platinum guide. I unfortunately left it in Maine, but I'm getting back soon, so I can provide an answer then. I don't think only one legend is released when you beat the Elite 4 because the capturing of legends doesn't correspond with any of the other legends, so I would assume (and I'm pretty confident) that any legends that can respawn after beating the Elite 4, not just one.
What do you think? I want to get a consensus.