In the first edition of Random House Unabridged Dictionary (1966), the entry they occupies eight lines and is trivial. In the second edition (1993), a long section on usage was added, which I will reproduce in full: “Long before the use of generic he was condemned as sexist, the pronouns they, their, and them were used in educated speech and in all but the most formal writing to refer to indefinite pronouns and to single nouns of general personal reference, probably because such nouns are not felt to be exclusively singular: If anyone calls, tell them I’ll be back at six. Everybody began looking at their books at once. Such use is not a recent development, nor is it a mark of ignorance. Shakespeare, Swift, Shelley, Scott, and Dickens, as well as many other English and American writers, have used they and its forms to refer to singular antecedents. Already widespread in the language (though still rejected as ungrammatical by some), this use of they, their, and them is increasing in all but the most conservatively edited American English. This increased use is partly impelled by the desire to avoid the sexist implications of he as a pronoun of general reference.”
The author then proceeds to rip these progressive dictionary fellows a new one. Archaic thinking? Or pragmatist against grammar anarchy?