Did the Giant Trinity A1 come with a derailleur hanger?
The rear derailleur hanger on the Trinity was not replaceable, it was part of the frame and was there at the time of production.



If there is no hanger on the end of the rear drop out then it has likely been either:


purposely removed (to make a single speed or fixie, possibly for track racing);
sheered off in a crash (or deformed and then removed); or
not an authentic Trinity frame.