A correspondent writes to say she had read an interview in Rolling Stone with the cast of AMC's Mad Men, where one of the actors said they had to be very careful with their pronunciation. 'There was no 'gonna' or 'shoulda' back then [in the 1960's:].' Could this be true?

It certainly couldn't. It's easy enough to check the point. These two forms actually get separate entries in the OED, and there we find gonna with a first recorded use in 1913 and shoulda with a first recorded use in 1933. (Als...