Largely, they'll be using in-house proprietary systems for their projections that we have 0 access to. You make it sound like they just grab guys and hope they are good. They're using the same systems that told them Ray was a great gamble at the right price, Matz was a good proespective option, etc etc.
No, that doesnt mean that every pitcher they grab will live up to their projections. No, it's not perfect, nobody claims it is. No, just because it's not perfect doesnt mean it's useless.