FLT CREW OF E145 BELIEVE THAT AN UNSCHEDULED ADDITIONAL FLT SEGMENT RESULTING FROM A FUEL STOP; ALTERED THEIR SCHEDULED ASSIGNMENT AND SHOULD HAVE MADE THE SUBSEQUENT LEG ILLEGAL IN THAT IT RESULTED IN OVER 8 FLT HRS IN THEIR DUTY PERIOD.

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OUR ORIGINAL SCHEDULE INVOLVED 5 LEGS THAT WERE CLOSE TO 8 HRS OF FLT TIME. ON OUR 4TH LEG (TUL TO DFW ON FLT XXXX). WE HAD TO DIVERT TO OKC FOR FUEL. THIS WAS DUE TO WX IN DFW. ON THE GND IN OKC; WE HAD LOGGED 6 HRS 20 MINS IN FLT TIME FOR THE DAY AND WERE SCHEDULED TO FLY OKC TO DFW ANOTHER 36 MINS (A BIT OF A LOW ESTIMATE) TO GET OUR PAX AND ACFT TO DFW. THIS FLT WAS ALSO FILED AS FLT XXXX. UPON REACHING DFW; WE FOUND THAT OUR GSO LEG WAS STILL ON OUR SCHEDULE. THIS SURPRISED US; BECAUSE IN OKC; ADDING OUR FLT TIME OF 6 HRS 20 MINS TO OUR 36 MIN SCHEDULE OF OKC TO DFW RESULTED IN 6 HRS 56 MINS OF SCHEDULED/ACTUAL FLT TIME AND ONLY LEFT 1 MIN 4 SECONDS FOR MORE FLYING. THE DFW TO GSO LEG WAS SCHEDULED AT XA30. SINCE THE OKC TURN RESULTED IN A SCHEDULE CHANGE; THIS EXCEEDED THE 8 HR LIMIT OF POSSIBLE SCHEDULES. WHEN WE CALLED SCHEDULING; THEY INFORMED US THAT SINCE THE OFF-STATION STOP USED THE SAME FLT NUMBER TO GET TO DFW; THAT IT WAS NOT CONSIDERED AS A SCHEDULE CHANGE AND SO WE COULD CONTINUE TO GSO EVEN THOUGH IT BROUGHT US OVER 8 FLT HRS. WE DID NOT AGREE WITH SCHEDULING AND SO GOT A CHIEF PLT REPRESENTATIVE ON THE PHONE TO INTERP THE RULE AND HE AGREED THAT WE COULD INDEED FLY THE GSO LEG SINCE THE SAME XXXX FLT NUMBER WAS USED FROM OKC TO DFW. WITH THIS APPROVAL; WE ACCEPTED THE FLT; BUT WANT TO FOLLOW UP ON THE INTERP OF THE EXTENSION RULE WITH AN INTERP IS OUTSIDE THE COMPANY (IE; PREVIOUS FAA RULINGS OR GRIEVANCES). DOES AN OFF-LINE STOP FOR FUEL THAT ADDS ANOTHER LEG TO THE ORIGINAL DEST RESULT IN A SCHEDULE CHANGE?