A MECHANIC AND HIS LEAD ARE INFORMED THE PASSENGER SEAT BACK AND TRAY TABLE REPAIR AND REPLACEMENT THEY DID ON AN A320; USING ROBBED PARTS; WERE ACTUALLY INCORRECT PARTS AND THE ACFT HAD FLOWN ILLEGALLY.

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I WAS WORKING A DEFERRED ITEM. ME AND MY LEAD WERE TOLD THAT THIS ITEM WAS OUT OF TIME. I WAS INSTRUCTED TO REPAIR THE SEAT IN QUESTION BY INSTALLING A SEAT BACK USING PARTS IN THE ONBOARD CONTAINER. I WAS ALSO TOLD THAT IF I WAS UNABLE TO COMPLETE THE REPAIR DUE TO PROB LOCATING PARTS; I WAS TO ROB THE NEEDED PARTS FROM ACFT X; LOCATED IN THE HANGAR. I REMOVED ALL THE PARTS ON ACFT Y. IT WAS QUITE OBVIOUS TO ME THAT IT WAS GOING TO BE IMPOSSIBLE TO REPAIR THE SEAT BACK WITH THE PARTS FROM THE ONBOARD CONTAINER AND FROM PARTS IN STOCK. I; AT THAT POINT; INFORMED MY LEAD AND FOREMAN OF THE SITUATION. I WAS AGAIN INSTRUCTED TO ROB THE SEAT BACK AND TRAY TABLE FROM ACFT X; WHICH I DID. THOSE PARTS WERE THEN INSTALLED ON ACFT Y AND THE DEFERRED ITEM CLRED. THE ROBBED PAPERWORK WAS COMPLETED BY MY LEAD. I WAS INFORMED LATER THAT ACFT Y WAS OPERATED ILLEGALLY DUE TO IMPROPER PARTS. SUPPLEMENTAL INFO FROM ACN 801721: ACFT Y WAS OUT OF TIME FOR SEAT BACK REPLACEMENT ON A DEFERRED ITEM. I WAS INSTRUCTED BY MGMNT TO ROB SEAT BACK FROM ACFT X. MECH REMOVED FROM X AND REPLACED ON ACFT Y. I; AS LEAD; CREATED AN ITEM TO COVER REMOVAL OF SEAT BACK. I WAS INFORMED LATER THAT ACFT Y FLEW ILLEGALLY WITH WRONG SEAT BACK PER PART NUMBER.