I am having a similar problem with American. I am booking flights on AA.com in guest mode, and when I put my BA# in it gives me an error message. AA Twitter said to just leave it blank and message them and they would add it. They did, but the flights were two weeks ago today and they didn't post at BA.
I think the issue is that BA has me as FIRST DR LAST and AA (and TSA) has me as FIRST LAST.
How do I get BA to understand the issue?