The Consortium first published The Unicode Standard (ISBN 0-321-18578-1) in 1991 and continues to develop standards based on that original work. The latest version of the standard, Unicode 8.0, was released in June 2015 and is available from the consortium's website. The last of the major versions (versions x.0) to be published in book form was Unicode 5.0 (ISBN 0-321-48091-0), but since Unicode 6.0 the full text of the standard is no longer being published in book form. In 2012, however, it was announced that only the core specification for Unicode version 6.1 would be made available as a 692-page print-on-demand paperback. Unlike the previous major version printings of the Standard, the print-on-demand core specification does not include any code charts or standard annexes, but the entire standard, including the core specification, will still remain freely available on the Unicode website.
What month did the Consortium first publish Unicode?