AA Cofounder Bill W., 1944:  

"The roads to recovery are many."

(The Grapevine, Sept. 1944, Vol. 1 No. 4.)

AA Cofounder Bill W., 1958:

Your President and other pioneers in and outside your Society have been achieving notable results for a long time, many of their patients having made good recoveries without any A.A. at all. It should here be noted that some of the recovery methods employed outside A.A. are quite in contradiction to AA principles and practice. Nevertheless, we of AA ought to applaud the fact that certain of these efforts are meeting with increasing success.

Address to the New York City Medical Society on Alcoholism, April 28, 1958.  Online at http://www.historyofaa.com/billw/med1958.htm

AA Trustee and Harvard Prof. George Vaillant, MD, 2001:  "Sixty per cent do it without AA."

Grapevine: You said about 40 percent of the people who remain abstinent do it through AA. What about the other 60 percent? Could we in AA be more open, more supportive of these?

George Vaillant: Yes. You know, if you're batting 400, it's all right to miss a few. I think the fact that AA knows the answer to an extremely complicated problem is probably all right.

But it doesn't hurt at the level of GSO for AA to have humility and understand that 60 percent do it without AA.

Complete interview in The Grapevine, May 2001, online in the Grapevine Digital Archive.  Brief excerpt here (PDF file).