DURING A NIGHT OP; A COMMUTER FLT ALERTS THE TWR TO THE FACT THAT THEIR TKOF CLRNC IS NOT VALID SINCE A B727 CARGO FLT WAS IN POS AND HOLD IN FRONT OF THEM ON RWY 27 AT SAN; CA.

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WE HAD TAXIED OUT FOR TKOF AND WERE #1 AT THE HOLD SHORT LINE ON THE N SIDE OF RWY 27 AT SAN DIEGO ARPT. AT THE SAME TIME; THERE WERE PAX CARRYING ACFT HOLDING SHORT OF THE SAME RWY ON THE S SIDE. THE CTL TWR RADIOED WHAT WE THOUGHT WE HEARD WAS 'ACFT X POS AND HOLD.' MY FO RESPONDED WITH 'ROGER; ACFT X POS AND HOLD.' AFTER ABOUT 1 MIN ON THE RWY IN POS; WE HEARD THE TWR CLR A COMMUTER PLANE FOR TKOF. WE THEN HEARD THE COMMUTER PLANE RESPOND WITH 'THAT'S ACFT X ON THE RWY.' THE TWR THEN INSTRUCTED US; 'ACFT X CLRED FOR TKOF' AND WE COMPLIED WITH THE CLRNC. I AM ABSOLUTELY POSITIVE THAT WE RESPONDED TO THE TWR WITH AN 'ACR X POS AND HOLD' RADIO XMISSION AND WE HEARD NOTHING BACK FROM EITHER THE TWR CTLR OR COMMUTER QUESTIONING WHO EXACTLY WAS SUPPOSED TO POS AND HOLD. IT'S POSSIBLE THAT THE COMMUTER MAY HAVE HAD A FLT NUMBER THAT WAS SIMILAR TO OURS AND IT'S ALSO POSSIBLE THAT BECAUSE BOTH OF OUR FLTS HAD FEMALE COPLTS WORKING THE RADIO; THE TWR MAY HAVE THOUGHT HE HEARD A POS AND HOLD READBACK FROM COMMUTER. IN ANY EVENT; THE BOTTOM LINE ON ALL THIS IS THAT EVEN IF WE DID ERR BY POSITIONING ONTO THE RWY; IT WAS AN HONEST MISTAKE THAT NEITHER THE TWR NOR COMMUTER QUESTIONED AFTER OUR READBACK TO POS AND HOLD. WE SIMPLY THOUGHT WE HAD CLRNC ONTO THE RWY AND WERE ROUTINELY COMPLYING WITH THE CTL TWR'S DIRECTIVE.