Originally Posted by JJeffrey

For sure they can still see your original fare basis, but IMO that shouldn't have anything to do with it. Unless something has seriously changed recently, flying AA to/from LHR connecting with BA shorthaul you have never had to pay any additional surcharges.

My hunch is many if these rate desk agents are just clueless or as equally in the dark as we are with this process, especially with the correct way to calculate any surcharge add/collects and when it should be applied.

Economy JFK-LHR-DUB has ~$100 in YQ while business has ~$1000. So it seemed the agent was trying to collect the full YQ difference even though that difference should not be applied since the majority is tied to the AA metal longhaul portion.

In comparison for a standalone BA LHR-DUB flight the difference in YQ between Y-J is about $6.