The 2019 release of City of Mist reorganized its core from one book into two, as explained in this FAQ from their product page on DriveThruRPG:
Why did you split the original Core Book into two books?
The original Core Book was simply too big and as a result both daunting for new players and unwieldy. We wanted to make City of Mist more accessible to everyone by releasing the core rules in one volume and the resources for MCs in another.
If I have the original Core Book, do I need the new books? What am I missing if I don’t get them?
The new books contain exactly the same content as the original Core Book, with the following exceptions:
The MC Toolkit contains a full ready-to-play case, Gambling With Death, that is only presented as an outline example in the original Core Book.
The new books have the Yellow Pages - summary and reference pages at the start of every chapter.
The content in the new books is arranged differently, with setting materials moved mostly to the MC Toolkit and the Core Moves appearing before Game Resources in the rules chapter.
The new books contain some corrections to errors found in the original Core Book.
I'm looking for some further clarification on this last point.
Is there a listing of the full errata somewhere? Are any of these corrections changes to the rules text or primary examples that are major enough to affect how you play?