You can talk about people being unaware of the pre-patch and expansion release schedules but everything about Shadowlands hasn't been by the book.
The time between the announcement of a release date and a release date was only shortened by WotLK release, historically announcements for release dates have been happening earlier and earlier before the release date. The last 3 expansions for example have all average something like a 110 day announcement window, this one was 61 days. (I wasn't able to find the exact date TBC release date was announced, the rest however are below).
WotLK release date was announced 59 days before it's release.
Cataclysm release date was announced 64 days before it's release.
MoP release date was announced 62 days before it's release.
WoD release date was announced 91 days before it's release.
Legion release date was announced 134 days before it's release.
BfA release date was announced 131 days before it's release.
Based on the expansions when Ion has been in charge, Legion & Battle for Azeroth (Ion took over lead half way through Warlords of Draenor), an October 27th release date should have been announced back in June on average.
The shortest a pre-patch has historically been is 4 weeks, we're now looking at breaking that record. By your own belief of the 'pre-patch and expac release schedules' the pre-patch should be hitting on September 29th.
So we can talk about precedent and history and 'figuring out the schedules' but nothing about the announcement of Shadowlands launching, nor the pre-patch has followed any historical schedule, unless you tie the announcement of the release date to elements of the game from a decade ago?