comes down to your own belief. most decks have one or two extra because they're printed on a sheet of 80. myself, i omit these two extra cards, some people leave them in as a way to show there's a new future ahead, or ongoing change in the present is making it hard to predict future events.
no that's fine, not all of them are numbered actually. but in a typical deck you have 78 cards, so there's going to be two extra, either blank, or have something written on it. you can use these card or take them out, it's up to you. think of them like the Joker cards in a regular pack of playing cards.