A B737 FLT CREW IS UNSURE IF THEY WERE CLRED FOR TKOF AT BOS.

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WE MAY HAVE TAKEN OFF FROM RWY 9 WHEN WE WERE TOLD TO POS AND HOLD! I DON'T KNOW FOR SURE EXACTLY WHAT WAS SAID! OUR TAXI CLRNC FROM BOS GND TOLD US WE WERE GOING TO DEPART ON RWY 9; BUT FIRST WE WOULD HAVE TO HOLD SHORT OF RWY 4L AND CONTACT BOS TWR ON 128.8. OUR INITIAL CONTACT WITH BOS TWR ON 128.8 WAS TO IMMEDIATELY CROSS RWY 4L BECAUSE THERE WAS TFC ON A 1.5 MI FINAL FOR THAT RWY. I COULD SEE THE LIGHTS OF THE ACFT THAT WERE ON FINAL FOR RWY 4L AND I KNEW AS LONG AS WE EXPEDITED ACROSS RWY 4L THERE WOULD NOT BE A CONFLICT; WHICH IS WHAT WE DID. BEFORE WE GOT TO RWY 9 WE WERE COMPLETING THE TAXI CHKLIST. SIMULTANEOUSLY; I ANSWERED THE INTERPHONE CALL FROM A FLT ATTENDANT SAYING THAT ALL THE FLT ATTENDANTS WERE SEATED FOR TKOF AND THE CAPT ANSWERED THE RADIO CALL FROM BOS TWR. THE CAPT TOLD ME WE WERE CLRED FOR TKOF AND HE WANTED THE TKOF CHKLIST. WE COMPLETED THE TKOF CHKLIST AND I DID (WHAT I THOUGHT WAS AN UNEVENTFUL TKOF) THE TKOF FROM RWY 9. AT NO TIME DID I HEAR ANYTHING FROM THE TWR ON THE TKOF ROLL OR CLBOUT THAT WOULD HAVE MADE ME BELIEVE THAT WE WERE NOT CLRED FOR TKOF. IN RETROSPECT; THE CAPT TOLD ME HE WASN'T SURE WHAT HE HEARD FROM THE TWR AND THAT WE SHOULD FILL OUT AN ASAP RPTING FORM. SUPPLEMENTAL INFO FROM ACN 595030: I NOTICED THAT THE ATC DEP CTLR SEEMED A LITTLE SURPRISED TO HEAR FROM US. HE SAID SOMETHING SIMILAR TO '...AH...ACR X...ROGER.' THIS GAVE ME HESITATION AND CAUSED ME TO REFLECT UPON WHETHER A TKOF CLRNC HAD BEEN PROPERLY RECEIVED AND ACKNOWLEDGED.