If they only have a small dark spot, it sounds like they quit early. Here is a playlist I created of candling day by day.
https://www.youtube.com/playlist?list=PL8AKDZ9NpcmHLecXHu6m5qhUIp67ldEnG
https://www.youtube.com/playlist?list=PL8AKDZ9NpcmHLecXHu6m5qhUIp67ldEnG