A B737 CREW MISSED THE PDC CLEARANCE CHANGE FROM A LOOP4 TO A OSHNN DEP WHICH IS THE USUAL CLEARANCE OFF OF THE LAX RWY 24 COMPLEX AT NIGHT. NUMEROUS PREFLIGHT DISTRACTIONS OCCURRED.

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ON TKOF FROM LAX WE WERE VECTORED INITIALLY OFF RWY 24L THEN ASSIGNED A DIRECT CLRNC TO PEVEE INTXN. WE INFORMED ATC THAT PEVEE WAS NOT ON THE LOOP4 DEP. THEY TOLD US WE WERE REASSIGNED THE OSHNN FOR NOISE ABATEMENT. THEY SAID WE SHOULD HAVE GOTTEN THE NEW CLRNC IN OUR PDC MESSAGE. WE MANUALLY ENTERED PEVEE AND THE REST OF THE OSHNN DEP AND PROCEEDED NORMALLY. UPON FURTHER REVIEW OF THE PDC MESSAGE; I DISCOVERED THE REASSIGNMENT WAS INDEED IN THE PDC MESSAGE AND I HAD OVERLOOKED IT. I FEEL THAT THERE WERE SEVERAL CONTRIBUTING FACTORS WHICH HELPED CONTRIBUTE TO MY ERROR IN PROGRAMMING THE FMC. FIRST; WE WERE RUNNING LATE. OUR ORIGINAL ACFT WAS TAKEN FROM US ON AN UNSCHEDULED ACFT SWAP. SECOND; IT WAS A QUICK TURN DUE TO THE LATE ARR. THE INBOUND FLT AND OUTBOUND FLT TO ZZZ WERE NOT ANYWHERE NEAR FULL SO THE OPS AGENT WAS HURRYING US TO GET OFFLOADED AND UPLOADED AS FAST AS POSSIBLE AND OFF THE GATE. THIRD; THERE WAS AN OFFLINE FFDO WHO CAME INTO THE COCKPIT TO SHOW HIS IDENT AND REQUEST A RIDE WHILE I WAS OBTAINING THE CLRNC AND LOADING THE FMC. ALSO; I HAD A PRESSING NEED TO USE THE BATHROOM SINCE WE HAD JUST COMPLETED A 3-HR BLOCK FLT AND I HAD NOT LEFT THE COCKPIT. FINALLY; IT WAS LATE AT NIGHT AND I WAS NOT AS ALERT AS I NORMALLY AM. ONE OTHER AREA OF CONCERN; ATC ADVISED US THAT ALL LOOP4 DEPS ARE ALWAYS REASSIGNED THE OSHNN SID AFTER XA00 FOR NOISE ABATEMENT. IN THE FUTURE; IT WOULD BE HELPFUL IF DISPATCH COULD RE-FILE US ON THAT SID IF THEY KNOW WE WILL DEPART AFTER XA00. DOUBLE-CHK PDC LATE AT NIGHT WHEN NOISE ABATEMENT SIDS ARE A POSSIBILITY.