I just try to identify if there is a method only probabilist here or if the evolution of these ratios follows a reality.

I put in red my prediction, I don't know what to do with this 1,45M "in transit" between FY2017 tracked and shipped.

Would this massive 1,45M explain the poor following shipments at Q1 2018 ?

No because 1.45m on shelves/in transit is not alot for a popular console.

To compare, at the end of 2016/2017 there were over 3 million PS4 on shelves/in transit.

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

There is a weird thing here. After multiple adjustements, we have a 2018 Q3 sales tracked at 9,21 for an official ship. at 9,41
I would have expected that Nintendo would massively overship that quarter (my final prediction was 10,6) because they bet most of their goal on Smash and Pokemon, but they did not overshipped it. At ~200000 units it was close to be sold out ??
Second : it would mean that stock in transit was close to run out at Dec 31th, so we can expect a very big Q4 ship. annoucement. Much more than the 3,4M I predict.

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.