Trek has a history of going back and forth on individual features from production year to production year.

For the 1993 Model Year, Trek switch the 2300 composite frame from thread (earlier models) to 1" threadless headsets). As far as I could tell, other Trek composite bikes still had 1" threaded headsets. The next year (1994), the Trek 2300 came with a threaded 1" headset, continued to use the threaded headset until 1997/1998 when the composite bikes were discontinued.

The 1994 Trek 1400 that I have came with a 8-speed RX100 group. The next year Trek downgraded to 7-speeds on the Trek 1400. The 1997 (last year of the bonded aluminum frame) Trek 1400 that I have came from Trek with a 7-speed RSX group.

I don't think I've ever see a Trek model that Trek offered both threadless and threaded headsets on the same model year.

I don't have any of Trek's all carbon frames, but I do have Trek steel, aluminum, and composite frames. Seems to me that if you want a Trek 5200 with a quill stem, what you need to do is study Bikepedia to see which model years came with quill stems, and limit your search to bikes of the particular model and model year that featured quill stems. Keep in mind that the 5000, and 5500 models from the same model year, may not carry the same type of headset.