The private party 'lets hide from the press' thing ...
IMO if they want a big flashy do with no press pictures surely they would be better keeping it low key - no official public announcement - and have everyone arrive during the day in their normal clothes (at whatever palace they're holding it in). Everyone can change into the glad rags in private. Yes more hassle but it's not that often is it? It's not like they'd have to be putting people up on air beds in the lounge.
It would be so much better than this ''Yoo hoo everyone! We're having a fabulous party tonight but we don't want you to see us .... so ... bugger off with your cameras, ya?''