A B737 FLT CREW MISSED A REVISION TO THEIR PDC CLEARANCE PRIOR TO DEP AND DEVIATED FROM THEIR CLEARED ROUTING.

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WE ARRIVED AT THE ACFT ON DAY 4 OF A 4 DAY TRIP TO FIND THAT THE FO'S R2 WINDOW WAS CRACKED. IN ADDITION; THE APU WAS ON MEL. MAINT WAS ABLE TO PROCURE A WINDOW FROM ACR Y; BUT FOUND THE WIRING FOR WINDOW HEAT DID NOT MATCH OUR ACFT. AFTER A FEW HRS OF DELAY; THE ACFT WAS SIGNED OFF WITH THE WINDOW HEAT ON MEL AND WE PROCEEDED TO PREFLT AND GET READY FOR OUR FLT. WE WENT THROUGH ALL THE PAPERWORK AND LOADED THE CLRNC WE RECEIVED VIA PDC INTO THE COMPUTER AND IT MATCHED THE FLT PLAN WE HAD 'SILOW1 SILOW FLG GCN.' SUBSEQUENTLY WE RECEIVED NUMEROUS AMENDED RELEASES (4 OF THEM); THE SECOND OF WHICH ADDED THE WINDOW MEL AND CHANGED THE FLT PLAN (WE DIDN'T CATCH THAT PART); THE THIRD CHANGED DRIFT-DOWN ALTERNATES AND THE FOURTH THE MINIMUM FUEL. BY THE WAY; THIS IS THE CAPT'S FIRST TRIP OFF OF OPERATIONAL EXPERIENCE IN THIS ACFT. ALSO; THE COCKPIT WAS VERY HOT AND THE GND AIR WAS INSUFFICIENT. DURING ALL THIS WE WERE PLANNING FOR THE CROSSBLEED START (CAPT'S FIRST) AND PLANNING ON WHAT TO DO IF WE NEEDED TO DO AN UNPRESSURIZED TKOF AS IT WAS GETTING PRETTY HOT AND WE HAD NO APU. ALSO COORDINATING WITH OPS CONCERNING TOO MANY DOGS IN FIRST CLASS. ANOTHER DISTR WAS THAT DISPATCH SENT US A SIGMET FOR VOLCANIC ASH ON OUR RTE. THE CAPT MADE 2 PHONE CALLS TO DISPATCH DURING THIS TIME AND THE CHANGE OF FLT PLAN DID NOT COME UP. NEEDLESS TO SAY; THERE WERE MANY DISTRS DURING PREFLT ALTHOUGH THE CAPT AND I WERE VERY SLOW AND METHODICAL DURING THE PROCESS TRYING TO MAKE SURE WE GOT EVERYTHING AMIDST THE CONFUSION. PUSH; START; TAXI AND TKOF WERE ALL NORMAL. CLBOUT OUT ON DEP FREQ WE WERE ASKED TO IDENT AND SUBSEQUENTLY ASKED AGAIN ON THE NEXT FREQ. THEN THE CTLR ASKED US WHAT OUR CLRNC WAS AND WE TOLD HIM. UPON FURTHER CHKING; WE DISCOVERED THAT ALTHOUGH WE WERE FLYING OUR PDC; THE SILOW1 ETC; OUR FLT PLAN SAID BXK2.PMD.J65; ETC; SO IT DID NOT LINK UP ANYWHERE. THIS CREATED MUCH CONFUSION AND WE COORD WITH ATC TO CONTINUE ON OUR ORIGINAL FLT PLAN SINCE THAT WAS WHAT WE WERE DOING AND THE WX WAS CLR (WX WAS THE REASON FOR THE FLT PLAN CHANGE BY DISPATCH; THOUGH IT WAS NOT A FACTOR ONCE WE WERE AIRBORNE). WE THEN CONTACTED DISPATCH AND COORD OUR RTE. THE FLT CREW NEEDS TO BE EXTREMELY VIGILANT WHEN REVIEWING CHANGES IN THE PAPERWORK AND NOT ASSUME THEY KNOW WHAT THE AMENDMENT IS FOR WITHOUT A THOROUGH REVIEW. IF THE FLT PLAN IS COMPLETELY OVERHAULED; IT WOULD BE USEFUL TO THE CREW TO GET AN ACARS OR RADIO CALL ALERTING THEM. I THINK WE WERE BEING VERY CAREFUL TO TRAP ERRORS; BUT THIS ONE GOT AWAY FROM US.