As I said in my original post, before they decided to go public, the Hellfire Club in the X-Men had gatherings. Not public gatherings but they did have them for their members. After all, Claremont based it on the legendary club in England only that Hellfire Club practiced black magic etc. If fact there is an episoce of the old Avengers show that Claremont borrowed heavily from since they drugged Emma Peel and made her their Black Queen. CBR's Brian Cronin did a column about it a while back.