^^
It's the retailers "overordered", not Nintendo "overshipped". It wouldn't make sense for Nintendo to ship less than the retailers asked for.
Think about the conversation below.
Retailers: "We want 900,000 copies of Zelda ST for launch."
Nintendo" "We don't think this game will sell that well. How about we'll give you 600,000 copies for launch then you can order a second shipment when it's sold out?"
MikeB predicts that the PS3 will sell about 140 million units by the end of 2016 and triple the amount of 360s in the long run.