Just thought would mention, normally for new product releases there are at least 2 distinct batches to arrive in stores.
First is air freighted typically not many units(often on pallets), second about a month later for the US, are standard shipping containers with the vast bulk of the supply. Air freighted products quite a bit more expensive (i looked at costs a couple of years ago and it was >5x).
If have just spent large $ on a production run, want to get some return as soon as possible but don't want to wreck quite often tight margins by air shipping too much and have it sit around for the month it takes the bulk to arrive. By selling out early can quite often get publicity and pre-orders to help shift the volume arriving later without having to discount the initial price too much.