Spectators can be seen watching the filming of the "New York, New York" number in Rockfeller Center (though it could be argued that the sight of three men in navy uniforms singing and dancing might attract attention, even in New York).
In the dance studio when Gaby tells Ivy what time to meet him, they both mouth "seven-thirty", but a voice overdub corrects both to "eight-thirty", which is the time Gaby set with the rest of the group.
When they are brought to a corner of the crowded night club, they are sitting at a round table. Next to them is a round table that has a burning candle stick. A girl is being swung around over them, blowing out the candle. When the 6 actors decide to get up and join them the candle which had previously been burned out is now lit and has a hurricane glass over it.
When the boys are looking for clues on the poster in order to find Miss Turnstiles they find her likes and dislikes. The only problem is none of that is actually mentioned on the poster they have or any that the viewer sees.