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Acquisition Incorporated is an odd duck of a book, I'd almost call it more of a Setting book, just a quirky and bizarre Setting (Office Comedy Realm Management).
I will add, the Wildemount book falls into a similar category as the Acq Inc book; both are almost entirely made by non-WotC staff, with WotC stepping in at the end to apply their rules for layout and other 5E book mainstays. Neither in my view really count as products that consumed the same level of resources on the WotC staff side, compared to any of the book releases in 2021.
Which kind of means that 2020 was a really slow release year (only 3 core releases by the core WotC staff) but we already know the pandemic delayed a development (Theros even had its print release delayed) so I suspect they may have pushed a product release to 2021.