I am in no way an expert on Star Alliance but their Lounge Acccess policy seems somewhat ambiguous especially when it comes to defining a Star Alliance-operated flight:
http://www.staralliance.com/en/benef...access-policy/
Star Alliance Gold Customers Travelling in Any Class: Customers have access to any Star Alliance member carriers' owned lounges with the Star Alliance Gold logo at the entrance.
Customer must present proof of Star Alliance Gold level status via a valid frequent flyer program Star Alliance Gold level card or other valid indication of Star Alliance Gold level status
Customer must also present a boarding pass for travel on a Star Alliance flight departing from the local airport
Others
Star Alliance flight: Flights operated under the two letter code of a Star Alliance member carrier
Boarding pass for a Star Alliance flight: Boarding pass must display the two letter code for a Star Alliance member carrier operated flight departing from that airport
Those 2 points under
Others seem to define a boarding pass for a Star Alliance flight (which is what you need for *G lounge access) as one that has a Star Alliance airline code on it and a Star Alliance flight as one that is operated under such a code.
I understand that implementation might be different from interpretation.