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You should be fine. It is very confusing lately with the merger between NWA and Delta. Eventually, WorldPerks (Northwest's frequent flier/rewards program) and SkyMiles (Delta's rewards program) will merge. They have already sent information (I got it via email about 2 months ago) regarding consolidating accounts, and I believe you are offered the ability to move Delta miles over to Northwest or vice versa. So I believe you may want to create a SkyMiles account (free) on Delta.com and then transfer your WorldPerks miles over to it. It might even be the case that you can specify miles to go to your existing WorldPerks account during the application process for the new Delta card.