so I've had my same day runs, for the first I had no problem getting all 4 BPs when I checked in within 24 hours of return flight.

second time, I checked in early and only got the 2 BPs for outbound. I could not check in any more at aa.com, nor I can view boarding pass there, even within 24 hours of return flight.

however, when I opened the AA iPhone App, it correctly showed inbound as not checked in and I could check in there... then at aa.com I could view BP again and had them printed out.

so I guess to get all BPs you would have to wait until 24 hours of return.