I don't see why once a year or 13k miles would be out of the question.
I would certianly send a sample off to the lab to confirm what the computer is saying though.
If the lab says 13k miles is ok than its ok. Modern engines don't really put a lot of crap into the oil.
You can run Delvac 1 in the old 606/603 diesels for 8k-10k miles without a problem, so you should be able to go longer with the new ones.