What if I need to check a bag from A to D? If I buy just the B to C segment now, is there a way to "combine" tickets later? (Is that even desirable or necessary?) Will I have to reclaim luggage at B and recheck it for the separately-purchased B to C ticket? And then again for the C to D?
I think you're asking for your bags to get lost. It's not just a matter of them putting the right tag on the bag. If you can't carry on and you have enough of a layover, I would try the recheck. Or, if you're feeling lucky...