I have had problems with DL and my WP# in the past. In my case, the number that they had on record for me was just plain wrong (numbers were switched around). When I brought this up at the gate, they told me that I must be mistaken, because "their system checks for that sort of thing, and it wouldn't have allowed the connection of an incorrect number to my name." When I showed them both my NWA WP visa card, as well as my NWA WP card with the right number on it, they still maintained that I must be wrong...
Anyway, I finally got the 3rd GA that I asked to change it (even though the other two claimed that it was impossible).

Also, I'm not sure that I want all of DL's elites getting upgrades on NW. I don't fly DL enough to take advantage of that benefit...