My theory is that they're linked once you have them. So if you have Brilliance and encounter someone with Fortitude then you should catch it. But lets say you have Brilliance and Magnificence and encounter someone with Magnificence and Fortitude. You won't catch Fortitude and they won't catch Brilliance as you are both 'locked' with Magnificence. Just a theory, but a friend of mine said he had one and then got another from a friend who only had the other one. Thats the only account of someone contracting another disease after already having one that I believe as its a trusted friend.But who knows, if we're meant to spread these around to open more clues on the OWLsector website then I'm guessing the lock is a mistake. I know, Bungie and Glitch? words you'd never see in a sentence right?