There are probably too many variations for them to figure this out along with TSA. The fact that AA have this straight is irrelevant. Their systems are always much better (and more bureaucratic) than UA. My daughter (Green card) got to check in as far as SFO the other night but had to check in at SFO the next morning for HKG (same ticket). The less you have traveled the less it seems to like you - though how a GS member gets caught under this non-rule of mine I cannot fathom. These kind of things kind of irritate me but the truth is one normally always have bags going overseas and if you are 1K you are not waiting in long lines generally.