B757-200 CREW HAD AN IMPROPERLY DEFERRED THRUST REVERSER. PLT LATER DISCOVERED THE ACFT WAS OPERATED INTO AN ARPT THAT HAD A RWY TOO SHORT TO COMPLY WITH MEL RESTRS.

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IMPROPER MAINT DEFERRAL. ON MAY/SUN/02; CAPT AND MYSELF DID A ZZZ TURN OUT OF ZZZ1. WE FOUND A DISCREPANCY IN THE MAINT LOG THAT WAS AN IMPROPER DEFERRAL OF A THRUST REVERSER. IT WAS IN THE LOGBOOK AND IN THE MIC SHEET; BUT DID NOT HAVE THE WHITE PLACARD IN THE FRONT OF THE BOOK. THE ITEM WAS NOT ON THE FLT PLAN WHICH MEANS THAT DISPATCH PROBABLY DIDN'T KNOW ABOUT THE ITEM. A FAILURE ON MY PART WAS NOT MAKING SURE THAT THE CAPT WAS INFORMED THAT THIS NEEDED TO BE ADDRESSED TO DISPATCH SO THAT THEY WERE IN THE LOOP. AFTER WE GOT BACK TO ZZZ1; MAINT FINISHED THE DEFERRAL CORRECTLY. THE ACFT WAS SCHEDULED TO CONTINUE ON TO ZZZ2. AS WE WERE LEAVING THE ACFT; THE MAINT CHIEF WAS IN THE GALLEY CORRECTING THE PAPERWORK; AND THE NEW FO WAS GETTING ON THE PLANE. I TOLD HIM ABOUT THE L THRUST REVERSER BEING DEFERRED SINCE THEY WERE GOING TO ZZZ2 AND THE MEL SAYS NOT TO BE DISPATCHED INTO A RWY THAT WAS 7000 FT OR LESS. HE AGREED. I DON'T RECALL SEEING THE NEW CAPT THERE; BUT I MIGHT HAVE MISSED HIM OR MY CAPT MIGHT HAVE ALREADY TOLD HIM. LATER THAT DAY; I WENT TO ZZZ2 WITH A DIFFERENT CAPT AND DIFFERENT PLANE. THE NEXT MORNING IN ZZZ2; WE GOT TO THE GATE AND SURE ENOUGH THERE IS THIS VERY PLANE WITH THE L THRUST REVERSER STILL DEFERRED. AFTER CONSULTING WITH DISPATCH AND MAINT; WE AGREED TO TAKE THE PLANE OUT; SINCE THAT MEL APPLIED TO LNDG THE ACFT; AND THE TKOF ACCELERATE/STOP PERFORMANCE NUMBERS ARE NOT BASED ON THE USE OF REVERSE THRUST. IN MAKING SURE THAT THIS IS LEARNING PROCESS NEXT TIME I WILL MAKE SURE THAT IF SOMETHING IS DEFERRED AND NOT ON THE FLT PLAN; A PHONE CALL TO DISPATCH WILL BE MADE.