Old subject but wanted to add to it. I emailed my contact at the GM Heritage Center and ask him if they had a document for the date of the Spyder and if there was enough documents to back this up. Here is his reply.
“It looks like the Olds Turbo-Rocket V8 was announced on January 7, 1962 and shown publicly for the first time on April 20, 1962 at the New York Auto Show. The Monza Spyder was announced on February 7, 1962. The release says the production would begin in April. As for when they were available to the public for purchase, our records don’t hold this information.”