The stats are stored in in the database. They are synced to the server for the purchased kepubs. But, for sideloaded books, they are purely in the database. It is in the Event table. Recreating them manually would be difficult as there are several rows per book that has been opened. And not all of the data is obvious. If you have a backup of the database from before reset, it probably would be possible to extract the data and load it into the new database.
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