Some answers
- Yes there can be contract lounges that typically are based on class of travel and then status with the operating airline, so you can be out of luck. These are pretty rare.
- Lounge economics is a dark art, but take it as passengers ticketed in the right class for the lounge are charged to the operating carrier. Passengers using status but say in Y where they could not access the lounge are charged back to the airline that provided the status. A good example is the QF F lounge in SYD, where QF has a children enters for free policy, but some airlines such as QR and CX do not so as a OWE travelling on QF your family can enter, but if on QR or CX they cannot as those airlines will not pick up the bill. This is usually through a charge back behind the scenes.
- Sometimes you get odd examples such as CX and BA that in MEL/SYD will use The House lounge rather than the QF J lounge. Arguments are on whether that is due to the QF lounges being poor or whether The House provided a better deal . Nothing to stop you using the QF J lounge.
- Some airlines organise lounge a little differently, QR for example will have a often a Qatar lounge (for J and F), and then a second lounge that is for elite members. Same with AA/BA at JFK there is a business lounge (Greenwhich), OWE (Soho and F pax on non AA/BA) and an F lounge (Chelsea - BA /AA F and GGL/CK only). Same with Qantas domestically will have in major cities a Business lounge for people in business class/OWE and a club lounge for those with status. It allows airlines to match perceived exclusiveness and domestic competition while still providing a lounge for OWS/OWE. The categorisation is simply what sign the airline choses to put on the door. I do not think there is any minimum standards for lounges.
- If you go surfing it is bad for the carrier that gave you the status. And I think that is why some airlines, CX for example give you a lounge pass, in the view that most people will be most likely to go to their preferred lounge.

That s in a nutshell, I expect someone else will be along with more details and examples.

KF