The New York Symposium Playing Cards were printed by U.S. Playing Card Co, and paid for by Ton Onosaka--they were done the year the convention was held in Japan. Not only were there about six different colored decks, but Ton also had stickers made the same size as card backs (minus the white borders) in another four or five colors. All impossible to find now.
As for "Spectacle," yes, this was written as the Sixth Symposium book. All the material was collected with that understanding. I thought it was quite devious when the book was published under a different title and there was no mention of what it was originally supposed to be.
In my opinion, by the way, number 5 is the best by far.