When you delete a user it does NOT delete any credentials associated with them.

To reuse a card credential from a deleted user you will need to go to that deleted user, then into their credentials, and manually delete the credential.

Here we will go over some steps to find, delete and reuse a card credential.

The easiest way is to use the Credentials page here - Reports > Credentials

Select the type of Credential you are looking for:

Now select the “User Status” dropdown and tick only “Deleted”:

Now we can use the Card Number search box to locate the particular Mifare Card:

If you selected a Wiegand Credential, the search has more options, here are two

Now click on the selected user and you will be taken to the Edit User Credential page where you can click the trash can and delete the credential from the deleted user:

Now you can assign that credential to another user.