Need Mai Kai Mystery Drink ephemera dates

I have been delving into the Mystery of the origination of the Mystery Drink. I think the first question: Who invented the Mystery Drink, is answered. It is, as we all long believed, the Mai Kai. Now there is a second question which is very much in the air. When?

The oldest Mai Kai drink menu, copyrighted 1957, does not include the Mystery Drink. Asking around at the Mai Kai, they thought it was started later, like in the 60s. Being that the Kahiki opened in 1961 with the Mystery Drink on their menu, the Mai Kai had to have started it previous to 1961.

Mimi Payne found that in her collection there was an Okole Maluna Club card hand dated 1958. That dates the Mystery Drink to a year after they opened. At Hukilau 2006, there was a lady at the Mai Kai who said she had been the original Mystery Lady in 1957 when they opened and was fired when they found out she was under aged. That really messed up the notion it started in the 60s. Did it start in 1957?

If you have in your collection:
The Mystery Lady postcards that is postmarked
The Okole Maluna Club mini menu that is dated
Happy Talk magazine with images or discussion of, the Mystery Drink
or other Mystery Drink items that are dated and in particular, dated 1957 or 1958, please post here.

I would love to get as close as we can to knowing when this milestone in tiki history happened.

The oldest card I have is postmarked Nov 1957, but it's not the mystery girl card and the mystery drink is not mentioned on the back. The mystery girl card that I do have is unfortunately not postmarked. I'm afraid this isn't much help, but the only other clue I have to offer from my cards is the phone number. The mystery girl card has the old LOgan 6-1513 number. By 1968 (from my cards anyway) the number was being printed as 565-6777. Wish I could be of more help. If you find the answer, please post it!