Digital/Vault
Treasure chests can be bought in the game's store for 500 gold each. Once bought, a chest must be opened and the new cards looked at. At that point the new cards are available in the Vault. They will be used when the game gathers together location decks. Having more copies of a card in your vault means you are more likely to find it during a scenario. Once in the Vault treasure cards can be salvaged for gold.
Each party has its own Vault. If you have 1copy of a specific card in your vault, then your characters can only have one copy of that card. However, if a character in Quest mode has this card but is not part of the actual party for this quest, the card can be encountered (and obtained) again.
If both of these characters are later in the same party, you have two copies of this card in your party.1