Originally Posted by
Globaliser
If it's a T5-T5 connection and it's less than 24 hours, then the bags can be through-checked. I'm pretty confident that I've seen reports here of people whose bags have been through-checked on an overnight T5-T5 connection even though that's not what they wanted, and something has had to be done to sort that out.
What I don't know are: (a) whether the time limit is the same for a T5-T3 connection; and (b) whether the check-in system will default to a through-check if possible. But there must be a possibility that both could conspire to catch out the unwary doing what the OP is doing - hence the suggestion to tell the check-in agent proactively to make sure that the bag is tagged how the OP wants it to be tagged.
I have done both T5-T5 and T5-T3 overnight connections many times over the years and have never had problems through-checking my bags. So you certainly can if you want to. I would also assume that you can get them back (I am usually asked if I want to through-check them). This is not necessarily true for AA on the way back (they have an eight hour limit or something like that so that if you are overnighting you have to pick up your bags and re-check them with BA the next morning). In the final analysis, I guess it depends on the agent doing your check-in.