I would phrase this a little differently. Allowing people in beyond those for whom the lounge is the default/recommended lounge will be based on expected numbers and follow a pecking order of sorts.

- They may very well let everyone in on some light usage days/times.
- They may refuse entry to all those who should go to another lounge by default if extremely busy times are expected

In other cases where they may be enough room to allow some people in beyond the default users but where it may not be possible to allow everyone who wants, in:

- Premier and GGL will likely trump every other non default user
- BAC card holders will take precedence over other One World eligible card holders
- For BAC, Gold will take precedence over Silver, and for other One World, Emerald will take precedence over Sapphire
- F and J flyers will take precedence over W and Y flyers
- Short time users will likely take precedence over people arriving hours before their flight.

So in short, if you are One World (non BAC) Sapphire travelling in Y and arriving quite early, you are the first one to be said no, if you are a BAC Premier flying in F on a partner which normally uses the TK lounge, you will be let in in the immense majority of cases.