When it comes to locos, I have always maintained that preordering is the way to go to ensure that you get what you want. I passed on a couple of items and now I am kicking myself because it has been several years and I have yet to see them come up for sale.
Rolling stock, not so much.
And I am at the point now where my wish list is VERY short and I don't buy trains nearly as much as I used to, as I am seeing reruns of a lot of previously released items, and they are not being offered in the road names I want.