So it means that they accept overshipments more easily for PS console than Nintendo ? that's weird, a PS4 box is 3 times bigger than a Switch's box
Basically overshipment usually coincides with sales ratio. Say, if you have a shop and sell 100 X (PS, Switch, Xbox, whatever) over a month then you order 100 more for the next month. These have to be delivered. Also for a console that sells 100 units over the month you reserve more shelfspace than for one that sells 10 a month. So really, the in shipments will usually about a month worth of sales or so (ship needs time, storage spaces at intermediary salesman and shelf space which amounts only to a little of this). A faster selling console will have bigger differences than a smaller one. As long as sales are increasing the stores are even more willing to err on the side of too much.
Holidays are special. Everyone knows you sell more than usual. So they order more. And going out of stock during the holidays is bad for business. So the last quarter usually sees more shipments while Q1 may be thinner if the stores can sell leftovers from the holidays.
So as PS4 was at the time at it's peak, it is quite well explainable, that it had a bigger shipment-sales difference. Switch will probably come there too.