After that first encounter I saw this cat again outside the concert place. This time it was an unusually hot day and the sun was very strong. She/He was sitting with tail curved around in the only shady spot near the front entrance.
As I approached and spoke, the tail unfurled and he/she responded in the typical "give me some attention" manner. As I was complying it occurred to me that it was too hot out for him/her and asked if she wanted to get back in. About then she was on the steps near the door so I buzzed the intercom. The door unlocked and she scooted right in when I opened the door.
Probably vastly relieved that someone had the good sense to come by to let her in (not that it would stop her from going out again of course). I could see the reception desk from the door and just yelled up that I was "just letting the cat back in". Which they took very matter of factly and went on with what they were doing as I closed the door.
Queen or King of the venue!