If you want to know the dates of WoW's Patches and expansion release simply look at its biggest competitor - Final Fantasy XIV.
Patch 8.2 Dropped on the Tuesday before Shadowbringers officially went live for everyone (Not including early Access pre-orders)
Patch 8.25 went live the Tuesday before Patch 5.1 in Final Fantasy XIV. Yes not a big patch, but they know that Final Fantasy does not release tier content in odd numbered patches so they didn't go big
Patch 8.3 is the odd one out but because of Covid, Patch 5.2 for FFXIV was delayed til february. It was originally supposed to release in January, which, GASP is when 8.3 came out
Shocking right?
Patch 9.0 released in October 13th and guess what - FFXIV patch 5.35 was announced for the 20th before blizz gave the patch date of theirs. This patch updated the Relic questline came out as well. Relics usually involve alot of player engagement to complete so of course things would be delayed to coincide with its release.
Square said they plan to release 5.4 in December no matter what so I believe that Shadowlands will drop shortly before the announced release date.
You want to tell me that blizzard do not plan their patch dates around other games, yet this would be too much of a coincidence not to be true.