Are you talking about iOS updates? Entering your Apple ID password is a security measure so that others can't update your devices without your permission. As to your missing content, did you backup your iPad as recommended before doing the update? If you did, your missing content should be in the backup.
I've lost data after updates but restoring from the backup I made before updating restored that missing data.
If you have no backup and the missing content is not stored elsewhere, it is unfortunately gone permanently.