ARTCC RADAR CTLR MISSPOKE AN ACR CALL SIGN IN A DSCNT CLRNC AND DSNDED AN ACR BE02 THROUGH THE ALT OF A COMPANY DH8. NEITHER THE RADAR CTLR OR THE DATA CTLR CAUGHT THE READBACK BY THE WRONG ACFT DUE TO FREQ CONGESTION. TFC VOLUME AND SIMILAR CALL SIGNS OF THE ACR ACFT.

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I WAS WORKING ZDV SECTOR 12; RADAR ASSISTANT. IFR CONDITIONS OVER MONTROSE ARPT; GUNNISON ARPT AND MARGINAL IFR AT TELLURIDE ARPT. AT THE TIME WHEN INCIDENT OCCURRED; 7 ACFT ON THE GND AT MONTROSE WAITING FOR DEP CLRNC AND 2 ACFT AT GUNNISON WAITING DEP CLRNC. LOTS OF FREQ CONGESTION AND BLOCKAGE DUE TO ACFT ON THE GND ASKING ABOUT DEP DELAYS. LOTS OF DATA BLOCK COVERAGE ON THE RADAR SCREEN DUE TO THE HIGH NUMBER OF ACFT OCCUPYING A SMALL AMOUNT OF AIRSPACE. ON FREQ ARE: ACR XAAB LNDG GUNNISON; ACR XCAB LNDG TELLURIDE; ACR XDRS LNDG MONTROSE; ACR XDEN OVERFLT TO DEN; ACR XDEG OVERFLT TO DRO; ACR XDFC DEPARTING MONTROSE; ACR DGEB DEPARTING MONTROSE; ACR DGEC DEPARTING ASPEN; ACR XCFN DEPARTING TELLURIDE; IN ADDITION TO NUMEROUS NOVEMBER ACFT AND OTHER ACRS IN THE AIR AND ON THE GND. THE RADAR CTLR INTENDED TO DSND ACR XAAB TO 17000 FT TO LAND AT GUC. ACR XCAB TOOK THE CLRNC BUT THE READBACK COVERED UP THE CALL SIGN. RADAR CTLR COULD ONLY VERIFY THE ALT. ACR XCAB LOST PROPER SEPARATION WITH ACR XDFC AT FL210 WHEN HE DSNDED THROUGH HIS ALT. IN ACTUALITY; THE RADAR CTLR SAID ACR XCAB WHEN SHE MEANT ACR XAAB BUT NEITHER THE RADAR OR ASSISTANT CAUGHT THE MISSPOKEN CALL SIGN. THE RADAR CTLR DID THE CORRECT THING BY EXPEDITING ACR XCAB DOWN TO GET OUT OF ACR XDFC'S ALT WHEN THE CONFLICT WAS NOTICED. OTHER CONTRIBUTING FACTORS: I WAS THERE ON THE D-SIDE FOR ABOUT 3 HRS WHEN THIS HAPPENED. THE ENTIRE TIME I WAS THERE; ABOUT HALF THE ACFT WE WERE TALKING TO AND WORKING; WE HAD NO FLT PLAN INFO OR THE FLT DATA POS COULD NOT KEEP UP. WHEN HE CAME BY WITH THE FLT PLANS; IT WOULD FILL 2-3 BAYS (25-35 STRIPS) AND ABOUT HALF WOULD BE 'DEADWOOD;' FLTS WE ALREADY WORKED WITHOUT THE PRINTED STRIP INFO. THERE WAS CONTINUOUSLY A WAITING LINE OF ACFT AT MONTROSE AND GUNNISON (TO GO IN AND TO COME OUT) AND THE FREQ CONGESTION WAS ATROCIOUS. CTLR HAD TO CONTINUOUSLY REPEAT CLRNCS 2 AND 3 TIMES WHICH IS TERRIBLE WHEN SO MANY CLRNCS NEEDED TO BE GIVEN AND ACKNOWLEDGED. WORST OF ALL WAS THE CALL SIGNS OF THE ACR COMPANY WHICH WERE SIMILAR ENOUGH THAT THEY SOUNDED SIMILAR AND WERE DIFFICULT TO SAY WHETHER IN COMBINED FORM OR BY INDIVIDUAL NUMBER.