M. Frary, have you ever considered collecting jack pines mid-summer (late July/early August)?
I don’t know how cool your summers are (just how cold your winters are haha), but guys who collect up north here say that pines prefer to be collected in the summer, rather than spring or early fall. Once the year’s growth has matured...essentially the same idea as a summer mugo repot.
Though for sure, timing doesn’t matter that much if the soil is so bad as to leave each of these pines bare-rooted upon collection.