In December 2022 I flew TRN/JFK on an IB Business Class ticket booked on BA using Avios. There were absolutely no problems with managing the reservation on the IB website, including seat selection. I will add the Iberia website isn't the most sophisticated and user friendly of airline websites but I found that to be a minor inconvenience. On the day I traveled, IB was experiencing significant delays and I missed my connection to JFK thru MAD. Once I arrived in MAD, IB customer service was excellent in accommodating me. They rebooked for the next day and comped a great overnight hotel (including dinner and breakfast) with round trip transportation. I would not hesitate to book IB with BA again.