Originally Posted by missdimeaner

I can only speak from my own experience doing LHR (BA) - ORD - 3 days then ORD - LGA (AA) before returning to London on BA - all 1 ticket booked as a multi city.
My bags were not oversized as per AA but the domestic leg carried my international baggage allowance at no charge. This has been the case for all my trips of this kind.
As far as I'm aware you should get your international allowance, but AA can set the dimensions so you might incur the oversize charge.