Crowds queue to see the TARDIS console at Longleat in 1983.
Ingrid Oliver, Peter Capaldi and Michelle Gomez at the Doctor Who Festival at the ExCeL in London, in November 2015.
Generally speaking, a convention, as we understand the term these days, is a meeting of a group of people who share a common interest and features a public appearance by an expert in the field (ie, one of the stars of Doctor Who), perhaps with some sort of presentation of props or footage, and/or the opportunity to buy related merchandise. So what about, for instance, Tom Baker’s book signing at the Cambridge branch of Dillons in October 1997? He might not have come in costume but he did have a full-size TARDIS with him, and the shelves were heaving with Who-related books, so technically it could be considered a very small convention.