We've identified a list of Requesters in ServiceDesk+ that have no login name, email, department, phone, job title, site or domain

For example:

(names and personal details removed, but they are the same person)

One of my colleagues in our Applications team has a script to identify these requesters, and will be marking them as inactive (reducing our current Requester count from approx 60000 to 30000)

What I would like to know is how these records are being created in the first place.

Our requester list is based on a daily Active Directory import. As you can see from the above, the (yellow highlighted) record was created, and has no username.  The one below has all the required details (including login name) and was imported from our AD

How did the yellow record get created?  As far as I can see there are only 3 other ways a record can be created.  

1) An external person emailing in, but this cannot be the case or they would have an email address recorded. 

2) A CSV import... I'm not sure which fields are mandatory but from previous discussions with ME, I understand Login Name is used as a unique identifier.  It seems unlikely that this wouldn't be required.

3) A technician created the Requester record (but would have has to have written the "Name" in the exact format as the imported user (eg: Surname, Firstname, with correct spacing, capitalisation etc. As we're looking at around 30000 records like this, it seems unlikely that this would happen so often)

What I want to know is:

1) Is there another way this may have been created, not listed above?

2) If not, is there a way of finding out how this record was created?  We would ideally like to stop it from happening if possible, but first we need to understand where they are coming from.