How many Big Books have been sold?

The October/November 2001 issue of Box 459 had an article on some Big Book sales milestones:

in 1973 copy 1,000,000 was given to President Nixon
in 1985 copy 5,000,000 was given to Ruth Hock (non-alcoholic), who typed the original manuscript
in 1990 copy 10,000,000 was given to Nell Wing (non-alcoholic), Bill W.?s longtime secretary
in 1996 copy 15,000,000 was given to Ellie Norris, widow of former trustee chairman John L. Norris, M.D. (non-alcoholic)
in 2000 copy 20,000,000 was given to the fellowship of Alanon

At the current average of around one million sales per year the total as of 2012 was probably around 32 million.