Thank you for your answer. I think I understood most of it. I have both bike with aheadset stems and quill stems.

The reason is that I'm making an exact replica of Lance's 1999 Tour de France bike. And he was using a Cinelli Oyster quill stem on his Trek.

If I understand you correctly, then Trek has been selling these frames with two different forks? Otherwise it wouldn't be possible. I'm asking mainly because I would hate to buy a Trek bike with an aheadset stem, in the perception that I could exchange it, just to figure out I need to source a different fork.