AA comped me to Platinum based on DL Gold Medallion (comparable 50,000-mile level). I sent a prinout of my statement from the DL Web site, which apparently was enough. They didn't ask me to challenge. (This was in April 1998. The challenge program did, if I recall, exist then.) They sent me four 500-mile upgrade stickers with my welcome letter.

The fact that my travel agent did the legwork, and may have used a non-standard channel at AA, may have helped. If you have that option, use it.