Good question, Warrior!

Every warzone unlocks more cards to be earned, but it doesn't remove the cards already unlocked. This means that the pool of cards your chest can reward you from will always increase.

It's important to note that lower warzones cards aren't worse than higher warzone cards. Unlocking more cards only means that you can create more possible strategies and depth for your gameplay!

See you on the battlefield! ;)
Over.