Basically when using detailed scan, the receiver spends more time on each transponder looking for channels. Some channels take an extra few milliseconds to lock so a normal blind scan would miss them. You will notice that a detailed scan will take longer.
Some transponders have data on them or something else other than TV or Radio Channels, that can be decoded by the receiver. If it says ok and you pay close attention you will notice that it has scanned in at least one TV or radio channel. If it says FAIL, it means that it has found a active transponder on that frequency but there are no TV or radio channels on it, or at least none that the receiver can decode.