The question to beat all questions...

...Mistress, Miss, Mrs or Ms: untangling the shifting history of women’s titles

Neither “mistress” nor “Mrs” bore any marital connotation whatsoever for Dr Johnson. When in 1784 he wrote about having dinner with his friends “Mrs Carter, Miss Hannah More and Miss Fanny Burney”, all three women were unmarried. Elizabeth Carter, a distinguished scholar and lifelong friend of Johnson’s, was his own age and was invariably known as Mrs Carter; Hannah More and Fanny Burney were much younger and used the new style Miss.