B737 FLT CREW FAILS TO RECOGNIZE REVISED CLRNC ON PDC. ERROR IS DETECTED BEFORE COURSE DEV CAN OCCUR AND CORRECT SID IS ENTERED IN FMC.

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WE WERE CLEARED VIA THE PDC THE OSHNN3 DAG. WE THOUGHT WE WERE CLEARED ON THE LOOP4 DAG. THIS IS HOW IT IS ON THE FMC: FLIGHT COMPANY #/ LAX ZZZ PDC COMPANY #/ LAX B/737/L 370 -OSHNN3 DAG- LAX LOOP4 DAG LAS J146 HBU EDCT. THIS IS VERY CONFUSING. WE ARE USED TO READING A CLRNC STRAIGHT ACROSS; NOT ON TWO DIFFERENT LINES. WHEN WE GET A PDC CLRNC THAT IS DIFFERENT FROM THE ONE ON THE RELEASE; BOTH SHOULD NOT BE SHOWN ON THE CDU. FIRST TOWER CLEARED US FOR TAKEOFF WITH A HEADING OF 210; THIS NOT BEING CLEARED FOR AN RNAV DEP. ALSO; LAX TOWER USED TO ASK THE CREW FOR THE FIRST FIX. IF THIS IS NO LONGER BEING DONE; THEN IT SHOULD BE. IT WOULD HAVE PREVENTED THIS FROM EVER HAPPENING. DEP CLEARED US TO PEVEE AND THE OSHNN3. ON CLBOUT IS NOT THE TIME TO BEGIN TRYING TO RELOAD THE CDU. ALSO; DEP SAID THAT THEY NEVER ISSUE THE LOOP4 BEFORE XA00L; SO WHY IS DISPATCH FILING US THIS WAY? HE ALSO SAID THAT COMPANY IS DOING THIS A LOT. I SUSPECT THIS IS BECAUSE OF THE WAY THE CLRNC IS BEING DEPICTED ON THE CDU. IF THIS POSSIBILITY HAS NOT BEEN BROUGHT TO EVERYBODY'S ATTENTION; THEN SHOULD BE.