Putting the numbered side down makes it a lot easier to figure out what you've got next time you do an adjustment. If the wear surface is good, point it up - if it's bad, chuck it. The shims are not terribly expensive and there's no guarantee that you plucked the sizes you'll need when you do the adjustment. Murphy's law says you'll need at least one shim for the job that you don't have in your hand. Don't forget that you might be able to use a couple from your own engine in another spot.