I play the tenor sax in honors band and in one of our pieces, call tatarian dances, in the third movement it has a G below middle C. I didn`t know this note was possible on a tenor sax. Is it a music flaw? or is it possible to extend my register?

when u say middle C, do you mean the one on the staff. If you do then that note is definately possible and it is not a music error. infact tenor saxs usually stay in that range, i know thats my main. you play it the same way as a G in the higher octave but without the octave key. loosen up your jawa bit the help get out the note.