The code is correct. The item has since been collected and I have the actual label in front of me.
The real curiosity is that the whole delivery sequence is for a normal street address.
My only guess is that it got into the wrong bag and ended up on the rounds instead of being taken directly to the post office.... but did that mean the driver went to the PO Box and knocked on the little metal door? And when no-one answered, scanned the attempted delivery?
I have since spoken to the person who collected the article - they showed the information to the lady in charge at the P.O. and asked how it could happen ... and they admitted they had no idea. (They know the lady in charge - who knows their stuff - and most of the staff, who are usually quite good.)