@Ant **********
There is no such thing as a 12 month non-O. There is a 90 day non-O visa. And then a 12 month extension. An extension is not a non-O, it's an extension. Any re-entry permit purchased is only valid for the stamp it is purchased for. So if you purchase the re-entry permit while you are on the 12 month extension, it will be valid if you leave during that 12 months. You would need to purchase it before you leave. It's for ANY exit and re-entry. But land borders do not sell re-entry permits. So if you want to use a land border you'd best go to your immigration office first.