What card you talking about? Some cards from latest releases are "short printed according to Upper Deck"... or "beckett" but there's not much proof...and considering all the mass-production these companies do, a SP could be /10,000, /1,000....?????
One that is #/100 you have it's own guarantee that it's shortprinted, only 100 in the existance, which is pretty good considering the amount of collectors in the world.... we sometimes over-look the importance of low numbered cards...