Technically, "from outside of the game" just refers to your sideboard, and cards that have been removed from the game. But in a casual setting it's usually used for anything.
The official stance is that in sanctioned tournaments you only own the cards in your registered decklist (or put another way, only the cards in your registered decklist exist). And outside of sanctioned tournaments, you own all the cards you own.
The official stance screwed up those cards anyway. The card clearly states to remove death wish from the game. Logically you should be able to use another wish to get it back. But they retconned it to say 'exile', and 'exile' puts cards into a place that is still 'inside' the game.
