Perhaps this is working as intended, but I have so many itineraries which involve next day return, and multi carrier. On the outbound, I have no problem with check-in as I check in with the operating carrier. For my return, (DL flights with DL confirmation no), I try to check-in 24 hours prior at DL.com, and your online DL checkin takes me to NW checkin, where NW site indicate outbound flight had already left and fail. When I try to check-in at nwa.com and specify the departing city, even though my return segment is operated by DL, NW website directs me to DL website for check-in but fails with different error messages.

Could DL design the check-in site so that we can specify the check-in departing city so that it won't go back and forth between the two(NW and DL) sites?

Jiburi