Originally Posted by epiding

it works even they check it all the way - you simply rip tags off of one in IAD. both work usually.

the WORST case scenario for all the above is if you are somehow involuntarily rerouted during an IRROP and forced to take another flight and enter the US via another gateway (e.g. ORD or NYC), but your bags somehow don't follow you. then your short-checked bag would get stuck in IAD. this would be the only reason the 'rip off in IAD' is safer since you have control and worst case ends up in DEN with you.

but this rerouting IRROP is rare. either option is normally fine.