I have received different parts of the boarding passes on my last couple of trips. I got the whole boarding pass back on YYZ-YVR. They kept the small stub portion and gave me the bigger portion of the boarding pass on YVR-SEL. They gave me the smaller portion of the boarding pass on SEL-YVR and kept the bigger portion of the boarding pass.
Last week I got back the whole boarding passes on YYZ-YVR and YVR-ICN.