It is always worth giving the helpdesk a call periodically as they can check the status for you.

SPL will be able to see the status of the upgrade but JFK may not be able to as apparently KL and NW work from seperate reservations systems and NW cannot always see the waitlist status on KL flights.....Hence the reason that we get to take the little peices of paper with us to confirm to the check in agents in the USA that we really have been upgraded.