Just to clarify, “Unknown” isn’t manually selected by anyone, it’s just a blank field. There are many reasons people might choose not to type something in the field before pressing upload. Check out https://forum.inaturalist.org/t/why-do-some-serious-power-users-add-so-many-unknown-observations/282
Personally yes I’d recommend starting with identifying older observations to avoid those situations where folks plan to add the IDs shortly after uploading.