Entities in the system are linked by Id numbers and whatever is in the admin portal with that ID number is what is shown throughout the system both currently and in the past.
If you change a User account from John Doe to Larry Doe. Then every checklist that John Doe ever did will now be associated to Larry and not John.
It is always best to make a current entity inactive or delete it and create a new one from scratch vs. trying to reuse old entities that are not in use.