Smart Group cannot "see" data in a Sheet?

I’m new to DT3 but not to much else!

  1. I’ve created a populated db “Books”. A sheet in it contains the data with some custom fields (single-line text).
  2. Smart Group “Next Book” is shown below.

Question: the smart group (i.e., query) does not return any values, WHY? It is as if the query cannot “see inside the sheet”. Spotlight does see the sheet. Bug/feature/or newbie user?

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Columns in a sheet are not the same as custom metadata defined Preferences > Data in DEVONthink 3 Pro and Server.