I ran across this guy's website. FYI, he wrote Nancy McKeon at this address and received the following autographed photo within about three weeks:
P.O. Box 6778, Burbank, CA 91510. See: http://www.toddsautographarena.com/nancymckeonsmall.html

Funny you should mention this today, Karen. I received the same photo from a Don Nicholason today, as well. How peculiar! :)