FLC OF MLG INFORMED DURING TAXI OUT THAT THEY HAD AN ACFT WHICH HAD BEEN TAKEN OTS. RETURNED TO GATE AND EXCHANGED PLANES.

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WE DEPARTED GATE AT ORD IN ACFT ABC. WE WERE 3 HRS LATE DUE TO LATE INBOUND EQUIP BECAUSE OF ORD WX. WE DID NOT RECEIVE A LOAD CLOSEOUT; SO THE FO CALLED LOAD CTL FOR A CLOSEOUT. THEY READ HIM THE CLOSEOUT NUMBERS AND WHEN HE REPEATED THEM BACK; HE INCLUDED THE TAIL NUMBER ABC IN THE READBACK. LOAD THEN INFORMED HIM THAT OUR TAIL NUMBER SHOULD BE CDE. A BIT OF CONFUSION FOLLOWED UNTIL WE DISCOVERED THAT OUR ACFT ABC HAD BEEN TAKEN OTS BY MAINT FOR A TIMED OUT MEL ITEM. WE RETURNED TO GATE AND CHANGED EQUIP. APPARENTLY MAINT TOOK THE ACFT OTS PRIOR TO US LEAVING THE GATE; BUT NO ONE WAS NOTIFIED; NOT THE FLC; THE AGENT; OR THE GND CREW. COM BROKE DOWN SOMEWHERE. IF THE FO HAD NOT READ BACK THE TAIL NUMBER IN THE CLOSEOUT; WE LIKELY WOULD HAVE TAKEN OFF IN AN ACFT THAT WAS OTS. I FEEL THAT IT IS IMPORTANT TO NOTIFY THE CREW IMMEDIATELY WHEN AN ACFT IS TAKEN OTS. I SUGGEST THAT IT BE HIGHLIGHTED TO ALL FLCS AND LOAD AGENTS THE IMPORTANCE OF CONFIRMING THE ACFT TAIL NUMBER WHEN COMMUNICATING LOAD CLOSEOUT DATA.