When I've flown IAH to ABZ same as you connecting to BA, I did not have to collect my bag. HOWEVER, in every case, the bag did not make it and I had to have it delivered when it came up on the next flight. Last year, I decided to do IAH AMS to ABZ and due to irrops out of IAH ended up with a 7 hour layover in AMS and once again the bag didn't make it. I think it is the ABZ curse! Good luck.