By default, WhatsApp Pocket only scan the currently existed WhatsApp chat message in the result view. If you want to recover the deleted WhatsApp message, you need to turn on "Scan with Advanced recovery mode" under product Preferences panel, and click reset button. Then the product will scan the deleted message fragment in the scanning process.

WhatsApp stores all the whatsApp message in the database file, when one record removed from the database, it's no longer displayed as data in the table by the database. As the database doesn't clean up the whole database data, the message content is still in some place in the database.