ACR DEPARTS WITH WRONG FLT NUMBER CLRNC. DID NOT RECOGNIZE WRONG PDC.

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DURING FLT PREPARATION THE CREW NOTED THAT A CLRNC HAD BEEN RECEIVED VIA ACARS THAT APPEARED TO BE CORRECT. AFTER TKOF; HOWEVER; WHEN THE DEP CTLR QUESTIONED THE XPONDER CODE AND REQUESTED IT BE RESET; WE RECHKED THE ACARS CLRNC MESSAGE AND REALIZED THAT IT WAS FOR ANOTHER FLT NUMBER. WE THEN CHKED WITH CTR AND LAX CLRNC DELIVERY TO MAKE SURE THAT EVERYONE KNEW THAT WE WERE ENRTE AND THAT THEY WERE ALL READY FOR US. I FEEL THAT IN PART THE PROB OCCURRED DUE TO A SCHEDULE CHANGE AS WE WERE CHKING IN AT SFO. OUR ORIGINAL SCHEDULE WAS TO FLY THIS ACFT FROM SFO TO LAX TO LAS. THE ACFT; HOWEVER; WAS GNDED AS IT ARRIVED THAT MORNING IN LAX AND WAS UNABLE TO CONTINUE TO SFO WHERE WE WOULD HAVE PICKED IT UP. THE FO DID NOT MAKE THE FLT THAT DEPARTED AT CHK-IN TIME (OUR DEADHEAD). HE LATER DEADHEADED ON ANOTHER CARRIER TO LAX. WE ARRIVED AT THE ACFT AT DIFFERENT TIMES AND EACH THOUGHT THAT THE OTHER HAD REQUESTED THE DISPLAYED PDC MESSAGE WHEN NEITHER HAD DONE THIS. TO PREVENT THIS IN THE FUTURE; WE SHOULD EITHER MAKE A CHKLIST ITEM; A GND CTL/CLRNC DELIVERY READBACK OF THE SQUAWK OR SOME OTHER POSITIVE ACTION TO ACKNOWLEDGE PROPER RECEIPT.