I'm on BA 125 tickets and usually I do have all my personal data in the booking, especially when I booked it on BA.com. Thanks for the hint about the email address, mine has not changed for a long time.
However now trying to amend my email address back to what it was has led me into "Error - The email address used must be unique. The email you provided has already been registered. Please enter a different email address and try again" despite various attempts and waiting some hours. Time to phone, I suspect :-/
< insert grumbling about the state of BA's IT >