ACR Y NON ADHERENCE TO ATC CLRNC (SPD RESTRICTION) HAD LTSS FROM ACR X. SYS ERROR.

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ACR X GOING TO BOSTON ASKED TO INCREASE SPD TO 300 KTS (FROM 270 KTS). ACR Y CLBING OFF LGA TOLD TO MAINTAIN 300 KTS OR LESS. 3 MINS LATER; AT LEVEL FLT; GND SPD SHOWED A DIFFERENCE OF 40 KTS AND THE ACFT GOT WITHIN 4.75 MI OF EACH OTHER. BACK ACFT TURNED 80 DEGS TO THE N AND THEN CONTINUED ON COURSE. SUPPLEMENTAL INFO FROM ACN 199216. THE PROBLEM SHOULD NOT HAVE HAPPENED AT ALL. 2 ACFT ENRTE TO THE SAME FIX. FIRST ONE (ACR X) LEVEL AT FL210 AND ASSIGNED 300 KTS. ACR Y CLBING OUT OF 170 FOR FL210 AND WELL IN TRAIL OF ACR X (APPROX 8 MI) GIVEN 300 KTS OR LESS. ONCE SPDS WERE FORWARDED TO THE NEXT SECTOR AND THE IN TRAIL WAS ACHIEVED; WE WENT ON TO OTHER BUSINESS. APPROX 2-3 MINS LATER; THE NEXT SECTOR CALLS AND ASKS FOR MORE ROOM BTWN THOSE 2 ACFT BEFORE THEY TAKE THE HDOF ON THE SECOND ONE. AT THAT TIME THE FIRST ACFT WAS SHOWING 360 KTS ON THE GND SPD AND THE SECOND SHOWING 420 KTS. THEN THE RADAR CTLR TURNED THE #2 ACFT HARD L; BUT SEPARATION WAS ALREADY LOST (4.5 MI). I THINK THAT POSSIBLY THE #2 ACFT WAS GOING A LITTLE FASTER THAN ASSIGNED. THE SPDS REALLY SHOULD HAVE WORKED. THE OCCURRENCE WAS RECOGNIZED AT THE SECTOR FIRST; THEN AT THE AREA SUPVR'S DESK.