The manuscripts -- to be auctioned in separate lots in a Bloomsbury sale -- were commissioned by the countess, who asked those in her circle to contribute anecdotes for a book to be auctioned for charity, The Times of London said.
The tales will be sold separately, Bloomsbury said. Among those expected to fetch a high price is the one signed by Christie, who tells of her failed attempt to convert her hair stylist into a fan.
In another tale, actress Dame Sybil Thorndike tells of a clergyman introducing her as a member of "the oldest profession in the world." She said she didn't have the heart to correct him for he knew not what he said.
Simon Luterbacher -- head of manuscripts and senior book cataloguer at Bloomsbury's -- said the stories "as far as we know ... have never seen the light of day."