There's typically no information about specific dates that DCL releases itineraries. The typical release dates in the past have been:
While difficult to predict, generally it's around 18 months out, and over the last few years DCL seems to have adopted this pattern for release dates on new cruises:
"Winter": first cruise in the new year up to April/May (not including spring Panama Canal and Transatlantic) – sometime between late September to early November
"Summer": cruises from about May to August/September (not including fall Panama Canal and Transatlantic) – mid February to early April.
"Fall": September until the end of the year (ending with the last cruise starting in the old year) – generally around May.
Of course, this may all be out the window, now, with the current situation. A lot depends on when ports reopen to cruise ships, and how much it's going to cost. As well, as what changes must be made regarding capacity limits and activities onboard.