Originally Posted by javabytes

This. You can check in and obtain boarding passes for up to three flights. If you have a 4th, it will simply show you a connection information document instead of a boarding pass. But checking in from the homepage and manually entering the departure city will let you check in for additional downstream segments.

So if you're flying AAA-BBB-CCC-DDD-EEE-FFF, check in once and receive BPs for AAA-BBB-CCC-DDD. Then check in again specifying DDD as your departure airport (once you are within 24 hours of that departure).