AN A300 CREW; TAXIING FOR TKOF AT BOS; MISINTERPED A TAXI CLRNC; REQUIRING ATC'S REQUEST TO 'PULL UP FURTHER' IN ORDER TO CLR RWY.

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HOLDING SHORT OF RWY 9 ON TXWY S AT BOS; WAITING FOR LOAD CLOSEOUT; WE TOLD TWR ON 119.1 THAT WE DIDN'T HAVE OUR NUMBERS YET. THEY TOLD US TO TAXI DOWN RWY 9; THEN TO TURN L ON RWY 4R; FOLLOWED BY ANOTHER L ON TXWY E. WE WERE TOLD TO HOLD ON TXWY E UNTIL WE GOT OUR NUMBERS. WHEN WE RECEIVED OUR CLOSEOUT; WE TOLD TWR; WHO TOLD US TO TAXI STRAIGHT AHEAD TO BE SEQUENCED FOR RWY 9; AND TO MONITOR 128.8; WHICH WE DID. WHEN WE MADE THE L TURN ONTO TXWY S FOR RWY 9; THE TWR CTLR ASKED US IF WE WERE GOING FOR RWY 9. THE TWR CTLR ASKED US IF WE WERE GOING TO BE ABLE TO HOLD SHORT OF RWY 4L; WHICH WE NEVER HEARD AS AN INSTRUCTION. WE WERE ACTUALLY CLR OF RWY 4L; BUT THERE SEEMED TO BE A LITTLE CONFUSION; DUE TO MONITORING A DIFFERENT TWR FREQ WITH UNCLR INSTRUCTIONS. WE DID ASK TWR ON 119.1 IF WE FOLLOWED INSTRUCTIONS CORRECTLY; AND THEY ANSWERED IN THE AFFIRMATIVE. SUPPLEMENTAL INFO FROM ACN 564533: AFTER RECEIVING NUMBERS; CAPT TOOK RADIOS WHILE I CHKED THE NUMBERS. I OVERHEARD VAGUELY THE TWR REQUEST THAT WE MOVE UP IN SEQUENCE AND MONITOR ANOTHER FREQ. I HEARD THE TWR ASK IF WE WERE 'ABLE TO MAKE THE TURN AND PULL UP FURTHER (ON TXWY S)...SHORT OF RWY 4.' AS WE PULLED FORWARD AND CLR; I NOTICED AN ACFT AT APPROX 500 FT ON SHORT FINAL FOR RWY 4L. I THEN WONDERED IF THE CAPT WAS TOLD TO HOLD SHORT OF RWY 4L ON TXWY E BY THE PREVIOUS FREQ. IF SO; WE DID NOT HEAR SUCH A XMISSION. IT IS ALSO POSSIBLE THAT I DID NOT HEAR IT BECAUSE I WAS HEADS DOWN CHKING THE NUMBERS.