Official shipment data.
like i said to intrinsic, its only ahead of PS2 if you ignore that PS2 was only available in Japan in its first 3 quarters.
The launch was staggered.... but you are exagerating here. PS2 had the market to itself in japan for 2 quaters tot 3 quaters.
Because it's easier to prepare launches by doing one region at a time. The PS4 had a staggered launch as well, in case you forgot.
Aligning the launches by region and then adding them up to global sales makes the most sense to do comparisons. Otherwise you are looking at nonsense like the early PSP vs. PSV comparisons that had people go "Oh, the Vita isn't doing bad. It's tracking at a similar pace.", when in reality Vita's worldwide sales were compared to only the PSP's Japanese sales, because the PSP had a differently staggered launch. Anyone who used the method of aligning launches by region could see how awful the Vita was really doing, because that method painted a more accurate picture.
Likewise, in the case of the PS2 vs. PS4, your comparison shows the PS4 ahead which implies that the PS4 has a realistic shot at matching the PS2. Aligning launches by region, however, shows that the PS4 has already fallen behind by a significant margin which puts the PS4's chances to match the PS2 at very slim to none. The latter method is a more accurate reflection of the situation and allows better analyses as well as predictions.
This whole aligning launches while it may make sense if looking at it from a particular perspective, doesn't really make sense to me in the grand scheme of things. At the end of the day when you look at the PS2, its said it sold 150M or whatever. No one is gonna be talking about where it was released first or second or which countries it was even released in or not. It sold this much, period.
I do not expect the PS4 to sell as much as the PS2 did, but thats because I belive the world we are in now has a lot more competing for consumers money than the world we were in in the time of the PS2. But at the end of the day, when the PS5 is released or the PS4 stops being made/sold, we will say it had sold X amount of units. Simple as that.
This whole aligning launch thing is just a silly way of downplaying how its performing. Kinda as silly as saying nintendo is going to go bankrupt or out of the gaming business because its wiiU was a disaster while ignoring that it has something called the 3DS on the market.
The whole launch aligning thing just doesn't make sense to me. A sale is a sale. Every generation markets and consumer buying habits change. But at the end of the day, a sale is a sale.
But hey, I know as usual we are gonna disagree with this whole thing. To me though, I just don't see it the way you do. Its never made sense to me before. And its not gonna start making sense to me now because as I have said when anyone looks back at any previous gen hardware, no one says anything about which region it released first or second.