ACR MLG DISPATCHED WITH OLD INCORRECT FLT NUMBER.

Narrative

WE ARRIVED LATE IN PIT DUE TO TSTMS AND HAD AN ACFT CHANGE. WE HAD 30 MINS IN WHICH TO GET A RELEASE AND PREFLT OUR NEXT AIRPLANE TO FLY FOR FLT XX FROM PIT TO TYS. I GOT OFF OF THE PLANE AND PROCEEDED TO OPS WHERE I GOT THE RELEASE FOR FLT. I THEN PROCEEDED TO THE GATE WHERE WE WERE INFORMED WE HAD A GATE CHANGE. I WENT TO THE NEW GATE AND NOTICED THE AIRPLANE HAD A DIFFERENT TAIL NUMBER THAN OUR ORIGINAL AIRPLANE. I MADE A MENTAL NOTE TO HAVE THE DISPATCHER SEND ME AN AMENDED RELEASE OVER ACARS. THE FLT WAS POSTED AS ACR FLT XX AT THE GATE. WE PREFLTED THE AIRPLANE AND RECEIVED A CLRNC VIA ACARS FOR FLT (XX) TO TYS. WE WERE GIVEN A CREW MEAL AND HURRIED TO GET IT EATEN WHILE THE PAX WERE BEING LOADED. AFTER WE STARTED OUR PUSHBACK WE WERE ADVISED OUR FLT NUMBER WAS CHANGED TO FLT (XY). IT WAS IMPOSSIBLE FOR US TO PUT THE NEW FLT NUMBER IN THE ACARS AS THE PAX DOOR WAS CLOSED. WE FLEW TO TYS WITHOUT INCIDENT USING FLT (XY) FOR ATC PURPOSES. IN THE CONFUSION WE NEVER DID RECEIVE OUR AMENDED RELEASE FOR THE ACFT NUMBER CHANGE AS THE ACARS WAS SET UNDER FLT (XX). THE LACK OF COM TO THE FLC'S IS BECOMING MORE THE RULE THAN THE EXCEPTION. OVER THE LAST DECADE EVERYONE HAS BEEN CHIPPING AWAY AT THE CAPTS AUTH BUT AS A CAPT EVERY TIME SOMETHING GOES WRONG I'M TOLD I'M THE ONE RESPONSIBLE.