BA rep was giving you the correct info -- your ticket numbers are not in the PNR in the BA system. You will need to have this fixed before you are allowed to board the BA plane at ARN! They might be able to do this at the airport, but it might take a long time and worst case you miss the flight. Luckily it is very easy to do ahead of time. Best approach is to phone the AA RTW desk and have them send the ticket numbers to BA. TAL is supposed to do this, but obviously hasn't. Having the printed out receipt with you at check-in is a necessity, and BA could easily fix it based on your receipt, but it depends on the goodwill and diligence of the agent. Better to take care of it now, with a phone call.