Fender sold out to CBS in 1965 ending the pre-CBS era. Although Leo and his team were still involved with making the basses, and 1966 pre-dated the cost-cutting measures later imposed by CBS, these instruments do not attract the same price tags as the the pre-CBS items.
I have a perfectly lovely 1966 P bass myself but I doubt it will ever be for sale in any future I can see at the moment. Never say never of course.