In nutshell, currently, it is not possible with us to share tokens across users, or prevent the same card from being stored again. We will generate a token every time we receive a request to tokenise.
We only store the card details (i.e. the 16 digit PAN) and we don't have a user profile on our systems.
We do not differentiate whether the same user is storing the same card or another user is storing the same card. Hence the token is created for every time you request a card to be stored with us.
A use case for different users to store the same card could be members of a family sharing a card.
We do have risk checks in place to prevent users from associating the same card with another email ID or storing more than a certain number of cards with a particular email ID. This is optional and we can enable this for you if needed to manage how people share cards among themselves.