Slightly more precisely, previous HOTM that are from 12+ months ago, and no chance at the current HOTM — at least that’s how it was in Beta.
There is, however, a 0.1% bonus chance for a new “secret” hero, who will be revealed when the event goes live.
There are details on that in: 🧪 Early Information on Tavern of Legends Event [Part of The Beta Beat v29]