ZDC CTLR EXPERIENCED OPERROR AT FL230 WHEN DSNDING ACFT BELOW HOLDING PATTERN TFC AND MISJUDGING SPACING.

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WORKING SECTOR 18 IN ZDC. 15 MI IN TRAIL REQUIRED BY NEW YORK APCH FOR EWR ARRS. RELIEVED FPL FROM POS WHO JUST PROVIDED APPROX 8-10 MI BTWN 5 EWR ARRS. THE DECREASE IN MI IN TRAIL REQUIREMENT WAS CAUSED BY 2 'QUESTIONABLE' RELEASES FROM THE WASHINGTON METRO AREA BY THE TMU. SECTOR 17 IN ZDC WAS HOLDING AN ADDITIONAL 2 ACFT FOR EWR; 1 AT FL230 AND 1 AT FL180 OVER KERNO. BOTH ACFT WERE POINTED OUT TO ME. PLACED INTO A 'NO NOTICE' HOLD BY APCH. PUT 8 ACFT INTO HOLDING OVER ARD AND STEFI. THE ERJ INVOLVED WAS THE ACFT HOLDING AT KERNO. DSNDED THE HS25 THROUGH THE ERJ; WHEN ATTEMPTING TO GET THE HS25 TO MEET A FUTURE XING RESTR THAT LIES BELOW THE HOLDING PATTERN AT STEFI. THE ERROR WAS DISCOVERED WHEN THE MACHINE FLASHED. INSTRUCTED ACFT TO STOP DSCNT AND RETURN TO FL240. ACFT IN HOLDING WAS DIVERGING; SO NO ACTION WAS TAKEN WITH HIM. ERROR IN JUDGEMENT I BELIEVED CAUSED THIS ERROR. CONTRIBUTING FACTORS; I BELIEVE; WERE TMU'S 2 PREVIOUS 'QUESTIONABLE' RELEASES CAUSED THE PREVIOUS CTLR TO PROVIDE REDUCED MI IN TRAIL TO APCH. 3 ADDITIONAL RELEASES WERE APPROVED BY TMU; 2 WERE CURRENTLY HOLDING AT KERNO; 1 WAS ENRTE. (THE REDUCED MI IN TRAIL PROVIDED TO APCH TRIGGERED THE 'NO NOTICE' HOLD.) THE CTLR HOLDING THE ACFT AT KERNO WAS HOLDING THE ACFT HIGH; WHICH HINDERED ANY TEB ARRS WHICH HAVE TO MEET A XING RESTR IN APPROX 40 MI. IT WAS A TEB ARR (HS25) THAT WAS INVOLVED IN THE ERROR.