Originally Posted by jsloan

UA and Seaborne (BB) have an interline baggage agreement, so it is possible for them to check it through. Whether or not the agent will do it is likely YMMV. Generally, I would expect them to interline it by default, as the transfer is less than 13 hours and not overnight, but since they removed the specific timelines from the policy, things seem to be more up in the air.