Connection Registration Question: intended behavior when client sends pass between NICK / USER combo

[mrryanjohnston]

Thank you so much for this valuable resource.

The docs state:

The PASS command is used to set a ‘connection password’. If set, the password must be set before any attempt to register the connection is made. This requires that clients send a PASS command before sending the NICK / USER combination.

What should servers do if they receive a NICK then a PASS before receiving the USER? Technically, the registration is not complete, and the NICK / USER combination have not yet been received. Has the client technically sent the PASS command before sending the NICK / USER combo?