I think the "does a first advance ticked give you lounge access" depends on which TRain operator ...operates the station you're at.

So if I get a 1st advance ticket on Virgin for EUSTON-PRESTON I can use the lounge at Euston as they are the main opeator at Euston.

When I've had a 1st Advance on Virgin from Edinburgh to Preston then I can't use the lounge at Edinburgh as it's a (whatever east coast line is these days) station.

Mind you at Preston the staff just ask "What's a lounge?" but that's another story.