SIMILAR NUMBERS WRONG ACFT RADAR HDOF TO ARTCC.

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AN ACFT DEPARTED IAD. COMPUTER IDENTED FLT AS ACR XX (BLUE RIDGE) TO UNKNOWN DEST. ZDC TOOK COMPUTER HDOF ON ACR XX (NO FLT PLAN). IAD APCH CALLS TO AMEND ACR XY FLT PLAN. I TOLD THEM I DIDN'T KNOW WHO ACR XY WAS. IADZ SAID IT WAS THE ACFT 25 MI N OF IAD. I SAID NO; THAT'S ACR XX DATA BLOCK. THEY SAID; NO THAT'S ACR XY AND IT SHOWED ACR XY ON THEIR DATA BLOCK. DURING THIS TIME AN ACR XY WAS CALLING ON FREQ. WE HAD ACR XY IDENT. SURE ENOUGH ACR XX DATA BLOCK 'FLASHED.' I GOT ZNY TO TAKE HDOF AND EXPLAINED THAT IT WAS ACR XY AND DIDN'T KNOW FLT PLAN. (NOTE: ZDC ONLY HAS 15 MI AIRSPACE BTWN IAD APCH BOUNDARY AND ZNY BOUNDARY.) A FEW MINS LATER IAD TRIED TO MAKE A MANUAL HDOF ON ACR XX. AGAIN; THEY DIDN'T KNOW WHERE FLT WAS GOING. THIS TIME I TOLD THEM TO KEEP FLT IN THEIR AIRSPACE TILL THEY GOT A CORRECT FLT PLAN. AS IT TURNED OUT THIS FLT WAS GOING TO PVD AND THE CORRECT DEP RTE WAS E OVER BWI; NOT N OVER HGR. SOMEHOW THE CONFUSION LEVEL WITHIN IAD APCH REACHED A NEW HIGH TODAY. THEY GOT FLT PLANS AND FLT IDENTS MESSED UP AND COULDN'T OR WOULDN'T FIX OR ADMIT TO THE MISTAKE.