If you not generally allowed in on non-ow codeshares are the Alaskian, JAL, EK cases stated as if they are exceptions? Think they don't refer to BA lounges anyway.
My question arises because of the change in status of Loganair and the start of the EI BFS-LHR service. Another example if, after 28th October next year, I am flying loganiar ex GLA on a BA codeshare will I be able to bring a guest into the Terrace as I can now?