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mariekes - suggestion - download Nir Soper's Search my File's and get it to look for epubs on your hard drives, its very fast doesn't need to be installed ==>>
Alternative to Windows Search For Files + Duplicates Search
But - if you inadvertently did a Remove selected formats (Alt/Del) when you had your entire library selected, and you selected EPUB from the formats list then all the EPUBS would be trashed - i.e. they wouldn't be in the recycle bin.
BR