B737-300 CREW DEP ON THEIR FINAL LEG OF THE DAY 1 SHORT OF FLT ATTENDANTS.

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CRM COM BREAKDOWN. I WAS UNAWARE OF ANY PROBS ON THE NIGHT OF THE OCCURRENCE. UPON RETURNING HOME; I RECEIVED A CALL FROM THE CHIEF PLT INFORMING ME THAT I POSSIBLY COULD HAVE FLOWN THE LAST LEG WITH ONLY 2 FLT ATTENDANTS. SIT BACKGROUND: (I RECALLED) #2 FLT ATTENDANT HAD BEEN WONDERING ALL DAY IF THERE MIGHT BE A COMMUTING FLT ATTENDANT TO MDW; SO HE COULD COMMUTE HOME. FAST FORWARD TO MDW TERMINATING THE ACFT. A DRUG TEST REPRESENTATIVE CAME TO THE COCKPIT ASKING WHERE 3RD FLT ATTENDANT WAS. THE FO AND MYSELF AFFIRMED HE WAS PROBABLY STILL IN THE BACK. WITHIN MINS; ALL PAX WERE OFF AND I DEPLANED THE ACFT AND LEFT. AFTER CHIEF'S CALL; I CALLED MDW INFLT AND REQUESTED 1 OR BOTH OF THE OTHER FLT ATTENDANTS CALL ME AT HOME. I RECEIVED A CALL AROUND XA00 FROM #3 FLT ATTENDANT WHO INFORMED ME THAT #2 HAD PERFORMED A JETWAY TRADE AND HAD GONE HOME. PERSPECTIVE: WHETHER COMPLETED APPROPRIATELY OR WHETHER LEGAL; A JETWAY TRADE WAS PERFORMED. NEITHER THE ON-COMING; OFF GOING; #1 OR #3 FLT ATTENDANTS NOTIFIED ME OF THE CHANGE. CONSEQUENTLY; NO VERIFICATION PROCS WERE FOLLOWED. ADDITIONALLY; IF I WOULD HAVE KNOWN; THE DRUG TEST REPRESENTATIVE COULD HAVE BEEN HANDLED DIFFERENTLY. END RESULT: THE FLT WAS FLOWN WITH 3 FLT ATTENDANTS; BUT I WAS UNAWARE OF THE CHANGE. JETWAY TRADES NEED TO HAVE AN ADDITIONAL STEP OF NOTIFYING THE CAPT (THROUGH SCHEDULING) IF THE CREWMEMBERS THEMSELVES CANNOT PERFORM THIS FUNCTION.