Thanks, Al. The reason I asked is that when I choose "link directly" (at least from DropBox), it returns a URL like this:
which seems like the one I want, where I can swap the file out and have the updated one reflected in the course(s). When I choose create an alias, I get this URL:
and I get that same URL when I choose Make a copy of the file. I also get that URL if I choose the file from the server repository and choose Create an alias.
So I think I have what I need. Hopefully this helps others because I had trouble finding this information when I was searching for it.