Release dates for games - including expansions - generally have some far off date when they’re first announced. Typically it’s December 31st, this one just happens to be June 30th. Then at some point after the game is announced, they announce the actual release date. We’re currently in that period between when the game is announced and the release date is announced. I know for certain that this is how expansions have worked for WoW for over 10 years, and likely since WoW was first released.
Based on current patch cadence, and the fact that the relatively public alpha is currently happening, most people are guessing that Midnight will be out in February or early March. That certainly qualifies as “several”.