This seems to be a perennial problem for many, including me. If my first flight is operated by AA then there's rarely a problem as I check in with AA and the API information entered via their website and confirmed via the AA app always seems to be all present and correct and is usually passed to BA intact. However, when it comes to BA it's a different matter altogether. As others have said, random pieces of information drop off. I will have the green tick immediately after completing the form, and when I next look at the booking there's a red cross and something needs to be re-entered. It's never been a real issue for me except on one occasion when flying via JFK where I couldn't get my JFK - LHR boarding pass because BA's systems insisted on seeing my Green Card, even for a flight to the UK.