Scenarios
The Administrative Contact authorises a transfer but the Registrant is challenging that
A Registrar is not participating in resolving an issue with a transfer. Several attempts to engage have been made by the other Registrar, including a message the Emergency Action Contact, to no avail.
Two registrants are disputing the right to a domain name after an inter-reigistrar transfer -- registrars went through the right process and have no further information to add.
Both registrants were acknowledged at some point in time as being registrants. Both of their names have appeared in Whois, but they now disagree as to who the true registrant is.
+ - Administrative and Registrant contacts are spread across two parts of an organization and there's a disagreement between them as to the validity of a transfer
+ - A registrant-claimant approaches a Registrar claiming that they are the registrant rather than the Proxy Service Provider to whom the domain name is registered
+ - One registrant is completely unknown to the registrars
A website designer registers a domain under their name on behalf of a customer for whom they build a website. They are challenged by their customer who claims to be the registrant but has never appeared in any Whois record at any time.
A website designer registers a domain under their name on behalf of a customer, and then goes out of business - causing domain to expire, leaving registrants to resolve the issue with a registrar who has never heard of them.
+ - Registrant says "I'm the owner, but I'm not in control of the name, here's why, help me get it back"
+ - Privacy services -- losing registrar doesn't remove privacy service, the gaining registrar can't validate the identity of the person registering the name
This is also the case for any other entity that's providing the privacy service -- resellers or other 3rd parties for example
Somebody registers a domain name as part of their job, does it under their own personal account, they and company part ways, which trumps?
Person works at the company -- maybe in the corporate account -- their contact info is listed -- they have left the company and access to the account and controlling email address is no longer possible