Maybe when Johnny Ola was down for the party he and Fredo snuck away? Maybe Johnny said I need a few minutes in Michael's bedroom and Fredo was lame enough to cover? No that doesn't make sense because Kay would have seen the drapes open when she undressed and took her jewelry off-
hmmm... someone must have come into the room while she dozed off but who would have known? I may go with Apple on this one and say FCC just didn't think anyone would ask questions? The drapes had to have been closed AFTER kay was already in bed!