No doubt about it - stealth is the first key to a successful raid.  If stealth fails, the effects of surprise are diminished - sort of.  This reconnoiter could last a couple of days to see where the horse herd is grazing each day.  Also, the raiders needed to know the usual egress and entrance to the village  that is most commonly used.  Its harder to track if the trail is already filled with hoof and foot prints.