Comment by RHSeeger

There are different kinds of tournaments. Some of them are setup so the really rare cards aren't even allowed, some put a limit to one (for, like, a black lotus), some disallow them, some are only the current cards, and some you get a set of random cards when you start. There's all kinds of different tournaments, and the ones where you're allowed to use those rare cards work under the assumption they're valid.

To be honest, I haven't been to a MtG tournament in decades, so take that all with a grain of salt. But it should be _relatively_ accurate.