If you don't have an email or a copy of the offer page or something like that to fax them "proof" you had the bigger bonus offer, you may be out of luck. I had to fax them something myself (but my case was 2 years ago and I did have a specific email to print/fax to them). This happened not only with NW, but with some other places liek SPG too --- seems like they all have multiple offers out there!