Swapcard, like many applications, uses the email address as a login.
An email address can only create and be linked to a single account.
Thus, if several people use the same e-mail address, only one account will be created (in this case, the details of this account will correspond to the last person registered with this e-mail)
It also means that if you import the same participants repeatedly, there will be no duplication as long as the email stays the same.
On the other hand, if you modify the other information (name, first name, description...), the participant will have to accept or refuse these modifications during his next connection.