Originally Posted by
ATOBTTR
It has to do with liability for lost/damage bags and also bag fees now. DL is still far more generous than AA is (though I think less generous that Star Alliance). AA won't even through check bags on separate AA tickets. If on separate tickets, AA will force you to claim bags and recheck between tickets. DL will through check on separate DL to DL and DL to several other partners, even if on separate tickets.
What you define as the bare minimum may well be driven by policy and each airline has their own. DL will through-check to several partners if on separate tickets, but will not do so (or at a minimum, is under no obligation to do so) on separate tickets for those airlines not listed here.
https://pro.delta.com/content/agency...e-policy-.html
Just for reference agents at AUS checked my mother and mine bags through across separate tickets. It was actually a brand new agent. She knew it could be done, but didn't remember how. Asked redcoat and two minutes later tags printed out.