When a family is moved to the Lead File, they are no longer part of your main Jackrabbit database. If that family registers with you again using the Online Web Registration form, a new family record will be created for them in your main Jackrabbit database.
The newly created family record is not related in any way to the Lead File record for the same family.
It is recommended to restore the family's Lead File record to the main database and then merge it with the newly created family record. This allows you to pull all of the family's history together.