We went through this when TSA started giving us a hard time about the name on Mrs benzguy80's tix not matching that on her passport. She goes by a shortened version of her given name but that wasn't acceptable to the TSA officers checking BP's. We hadn't anticipated that when she applied for a AAdvantage membership some years back.

To resolve this she called AA who instructed her to fill out a form and sign in the presence of a notary before returning to AA. Once the form had been returned and processed the given name showed up her AAdvantage account and on boarding passes.

HTH,
benzguy80