How secret were Andrew Wyeth's Helga Pictures?

Andrew Wyeth's "Helga pictures" -- a cache of some 240 works, including nudes, of a single model done between 1970 and 1985 -- stunned the art world when they were revealed in the mid 1980s, inspiring a show at the National Gallery. And the collection created a further stir when it was bought by a Philadelphia businessman for several million and sold three years later to a Japanese buyer for tens of millions.