I think the info is in the "ExtraData" column. Unfortunately, that is a blob and needs to be decoded somehow. Exporting the value and looking at it in a text editor, it is probably a serialised object. You can see some names and interpret some values, but not all.
My guess would be that the 1021 stores the start time and 1022 stores the finish time of each reading session for a book. Then the total time for the book is the difference of the pairs summed together. And the total read is the total of these for all books. But, the total for each book might be put in the 5 event record when it is finished. That would make sense as the books finished count is the count the 5's, not the count of books marked as finished in the library.
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