Some of the 14 Stations of the Cross have no clear basis in Scripture; are they handed down by tradition?

Yes, they are handed down by tradition. Take Veronica, for example. In my commentary I do have a place, I think it is in Luke, where we figure that is where Veronica comes in, but her name is not mentioned. So if there is any mention in Scripture, that is it, and the rest comes to us through tradition. You will have to get my Luke commentary to see it; it is at the end of the commentary.