Don't know all the rules... don't really care. But, when I had kids/ friends with apps in at Delta, I was aware of sick leave usage. Not near as close as what you guys are talking about...much more grey. I wondered if MY sick leave usage( which Delta can and has a right to see) might be perused (as a recommended endorser) for the applicant. I know this will be poo-pooed by some, but the apple doesn't fall far from the tree and birds of a feather....
When you have 20,000 highly qualified candidates for 500 positions what does one use for discrimantors? As far as flows go, ask the Vatican how well it works out passing one person from system to system( settle down, not drawing a parallel between the two other than in principal.)
As a business person and employer, I would readily use discriminators like this ( when legal and cheap to vet) to weed out candidates when it's a " buyers" market