B757 Undifferentiated or Other Model
Human-Machine Interface; Communication Breakdown; Confusion
ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Human Factors; Procedure; Aircraft
I was the FO for the flight to ZZZZ.  We received our pre dept clearance [via] CPDLC. Apparently they had a significant reroute for us and all three pilots didn't realize the only way we would know this is by using the load prompt.  We were unable to print the message and didn't realize we had to go to the next page to see the load prompt. We discussed the clearance and we all thought it was as filed to ZZZZZ.  I departed the cockpit for a few minutes to use the restroom and while I was gone the capt and [relief first officer] saw the load prompt and discussed that we [already] had the route loaded and disregarded it. I returned and other cockpit duties raised and they forgot to ask me if I knew what that meant.  I remember from the training videos and bulletins that the load prompt was important but I had yet to see it since the new procedure came about.  We pushed back with the route to ZZZZZ in the box. ATC assumed we were cleared to ZZZZZ1 ZZZZZ2 ZZZZZ3 ZZZZZ4 ZZZZZ5 ZZZZZ6 ZZZZZ7.  After departure we we[re] cleared direct ZZZZZ1 ZZZZZ2. We responded we didn't have that for a clearance. It caused some initial confusion between us and atc but they gave us a heading until it was figured out. The capt went back to the CPDLC page and pressed load. Sure enough there was the new route. Atc gave us a phone number because they were just as confused as we were. After discussing the issue with atc over the phone the mistake was realized. They showed concern that pilots do not get any kind of warning that the route has changed. Before we used to get a 'revised segment' on the PDC. Now there is just a load prompt and that is it!!!  At no time did we bust an altitude or have a separation issue.
This aircraft was unable to print clearance; so all 3 of us read the pdf clearance before accepting. The Clearance stated Cleared flight route ZZZZZ; after ZZZZZ cleared flight plan route. Clr via ZZZ1 climb via sid. We interpreted this to mean we were cleared as filed; which was ZZZZZ- ZZZZZ1-ZZZZZ2-ZZZZZ3-ZZZZZ4; we did not notice a LOAD prompt on bottom of either page 2 or 3. Not real sure to be honest what page it was.
An international B757 flight received their PDC clearance via CPDLC and noted it contained no 'revised segment' annotation although there was a 'LOAD' prompt on one of the CDU displayed pages and opted to leave their filed route programmed in the FMS.  After takeoff ATC cleared them to a fix that was not in their filed route at which time they learned the route had been revised and was available to them had they activated the 'LOAD' prompt.