At least OW is a bit more flexible than say *A which only allows access from the departing airport of your J/F flight... but, I think alliances in general need to be more explicit with their lounge access policies (ST probably is the closest). They are the industry, they should already know all the different ticketing scenarios possible and should make a comprehensive official guide as to lounge eligibility, maybe in a table format which needs to be present at all lounge reception/entry areas.