What happens if several people register with the same email?

Expo platform, like many other event platforms, 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 information (name, first name, description ...), these fields being system fields will be updated (across the events) and the participant will be able to login using the same.