messages sent over to PACS from the site have 'O' for the residency code

Based on the setup in CCG you can only have two residency codes, 'I' or 'O' when messages file through there. If an 'I' is sent in then it will be 'I' everything else will be 'O'.

It was found that the accessions mentioned have 'O' for the residency code.

The reason patient class is going to Unknown is patient discharge messages filing into CPACS. This will move the patient class from I/O to Unknown, since the prior patient location can’t be true after the patient is discharged.