I found a history of The Chambers Dictionary online. Most of the editions of what used to be called The Chambers Twentieth Century Dictionary were not given an official number. The first to be numbered was the 7th, published as the Chambers English Dictionary in 1988. The next edition, the 8th, was the first to use the TCD name, and was published in 1993. Then there was the 9th edition in 1998, and the confusingly named New 9th edition in 2003, followed by the 10th edition in 2006, the 11th edition in 2008, the 12th edition in 2011, and the 13th in 2014. There was a revised 13th edition, which appeared in 2016, and this is the edition referred to in Listener preambles.