LESS THAN STANDARD SEPARATION BETWEEN MIL ACFT AND ANOTHER IFR ACFT. OPERATIONAL ERROR.

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I WAS WORKING THE R05 POSITION; BOSTON ARTCC. I ACCEPTED A HDOF FROM ZNY ON MLT X NE BOUND DSNDING TO 8000' LNDG AT SWF WITH OPPOSITE DIRECTION TFC SBND; 15 MI AT 7000'. I ISSUED A DSCNT CLRNC TO MLT X TO 4000' AND TO EXPEDITE DSCNT THROUGH 6000'. SEVERAL SECS LATER; I ASKED MLT X HIS RATE OF DSCNT AND THE PLT STATED 2000 FPM. AT THIS TIME; X WAS ISSUED A TURN TO AN 090 HDG (APPROX 80 DEGS RIGHT) AND THE SBND 7000' (ACFT Y) WAS ISSUED A TURN TO A 270 HDG (APPROX 90 DEG RIGHT). THE SBND 7000' PLT STATED TFC IN SIGHT. THE ERROR DETECTION MACHINE ACTIVATED ABOUT THE SAME TIME THAT I VERBALLY ASKED X PLT TO VERIFY THAT HE WAS INDEED LEAVING 6000'. THE SUPVR ON DUTY DID A TAPE MONITOR OF THE INCIDENT AND MLT X PLT DID ACKNOWLEDGE LEAVING 6000' 3 SECS PRIOR TO THE ERROR DETECTION MACHINE BEING ACTIVATED. THIS WAS VERIFIED BY THE AREA MGR IN CHARGE OF THE CTL ROOM AND HE CONCURRED THAT NO OPERATIONAL ERROR HAD OCCURRED. THE FOLLOWING DAY; THE 'QUALITY ASSURANCE' OFFICE DID A COMPUTER PRINTOUT ON THE TARGETS OF THE ACFT INVOLVED AND THEY DETERMINED THAT AN OPERATIONAL ERROR HAD OCCURRED SEVERAL SECS PRIOR TO THE VERBAL RPT AND 10 SECS PRIOR TO THE ACTIVATION OF THE ERROR DETECTION MACHINE. TO THIS DAY; I HAVE RECEIVED NO EXPLANATION AS TO HOW THIS COULD OCCUR OR WHICH SYSTEM IS MORE ACCURATE IN DETERMINING THE ACTUAL POS OF THE ACFT OR HOW THE QUALITY ASSURANCE OFFICE CAN OVER-RULE THE DECISION OF THE AREA MGR. THEIR ANSWER TO ME WAS; 'A DECISION HAS BEEN MADE AND IT'S NOT OPEN TO DISCUSSION. THERE WERE OTHER VARIABLES INVOLVED WHICH WERE ALSO NOT OPEN TO DISCUSSION.