Not every ship has a dedicated Concierge Lounge. Can't really say how they handle their Suite and Diamond Plus cruisers, since we tend to avoid those ships.
We were on the Jewel OTS in October/November, and there were HUNDREDS of D+ members on board. The Concierge Lounge is very small, so they used the Vortex Lounge as their "overflow" CL. There were crew members at the door checking SeaPass cards to make sure only Suite and D+ folks got in. Also, if you wanted to use the CL on deck 10, you had to insert your SeaPass card in the lock, just like getting into your cabin.
For Suite and D+ guests using the CL, there are complimentary cocktails, wine, champagne, beer, plus hot and cold hors d' ouvres (sp) from 5:00 to 8:30 p. m., plus they have a small breakfast offering (no hot stuff). Can't really say what they get in the Diamond Lounge - don't use it.