Aren't most of these messages self explaining?
In general you can only archive documents which are business completed, if a goods receipt quantity less than the issued quantity then you have stock in transit and must not archive such POs as someone has to complete them with another receipt that.
A lock at a PO item has the purpose to restrict any further activity with this PO until the lock is removed again, this includes restricting such POs from archiving. If someone thought that a lock is smart solution because he could not set a deletion indicator then he certainly was on the wrong track.
Pleae read the OSS note 401318 - Archiving: Additional information
and discuss the messages together with your MM consultant, the log usually shows a PO number on the right, so you always have one PO as a reference for each message to analyze the case in more detail.
Also search SCN, as most of these messages have been discussed before