AN ACR B757 FLC STARTED THEIR TKOF ROLL BASED ON AN ATCT LCL CTLR'S XMISSION; BUT NOW REALIZE THAT THE XMISSION MAY HAVE BEEN FOR ANOTHER COMPANY ACFT.

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WHILE IN POS AND HOLD RWY 27R; BELIEVED TWR SAID; 'FLY HDG 255 DEGS CLRED FOR TKOF.' READ BACK TKOF CLRNC AND COMMENCED TKOF ROLL. A COUPLE OF THOUSAND FT INTO TKOF ROLL TWR SAID; 'FLY HDG 250 DEGS AT THE MM; CLRED FOR TKOF.' RESPONDED; 'WE'RE ROLLING' AND CONTINUED TKOF. CAUSE: PREVIOUS ACFT TO TKOF WAS A COMPANY ACFT WHO WAS GIVEN 255 DEG HDG. THE TWR XMISSION WE BELIEVED TO BE OUR TKOF CLRNC WAS ONLY ABOUT HALF AS STRONG AS THE TWR'S NORMAL XMISSIONS. I HEARD; '255 DEG HDG...' FOLLOWED BY SOMETHING INDISTINGUISHABLE. I INTERPRETED IT TO BE; 'CLRED FOR TKOF;' BUT WAS PROBABLY; '...CONTACT DEP.' THIS MISINTERP COULD HAVE BEEN AVOIDED IF I HAD INSISTED ON A LOUD AND CLR TKOF CLRNC OR QUERIED THE TWR PRIOR TO BEGINNING TKOF ROLL. OTHER CONSIDERATIONS: 1) IN THE PAST I HAVE EXPERIENCED AND WITNESSED OTHER ACFT CONTEND WITH OCCASIONAL POOR RECEPTION WHILE 'IN POS' ON RWY 27R. ACFT HAVE HAD TO RECEIVE TKOF CLRNC FROM ACFT ON THE TXWY; RELAYING FROM THE TWR; OR THE ACFT IN POS HAS HAD TO MOVE FORWARD TO GET OUT OF A 'DEAD ZONE'. THIS MAY HAVE CONTRIBUTED TO OUR RECEPTION PROB. 2) ON OUR TAXI OUT I NOTICED THE TWR CTLR SEEMED TO HAVE TROUBLE KEEPING TRACK OF ACFT TAKING OFF. IN ONE CASE THE TWR CLRED AN ACFT TO TKOF WHEN IN FACT IT HAD ALREADY DEPARTED AND WAS WAITING FOR PERMISSION TO CONTACT DEP. ALTHOUGH I DO NOT HAVE ANY OTHER SPECIFIC EXAMPLES MY GENERAL FEELING DURING TAXI OUT WAS THAT THIS CTLR WAS NOT KEEPING GOOD TRACK OF THE 'TKOF' ACFT UNDER HIS CTL.