Without further setup, cards added through a mod will always show up in the collection with their specified discovery state (i.e., if a card is marked as undiscovered in the code and you discover it, it will once again be undiscovered after restarting the game. To prevent this, insert the following code (taken from Game:init_item_prototypes) after adding your cards in your init function:
#Added cards and discovery state in the collection
round scroll