Ah my apologies, I didn't realise you couldn't see the forum without registering. The data was gathered by taking the graph you shared and adding on the newer figures from this updated graph from CD Project Red:I don't see this post, but it seems I would have to register to see it anyway. Looking into those numbers for verification which you should also do) that's not from CDproject at all, and it seems to be the forums guessing data.
I also find it curious how they have the PS5 close to 15.5 million, which is 4.5 million more than the 2019 total despite the sales shrinking down considerably during 2019, while the Xbox One basically stopped after adding only slightly more than a million more.
This isn't accurate data, even VGchartz has a lower number, and they are quick to correct when real data comes out, so that means that even they haven't found this 1.8 million.
You say the claimed update was as of 2021, but in 2021, the only sales news was that the Witcher 3 sold 30 million, and it sold 28 million later in 2020, So you getting a total of 43 million added together is impossible for 2021, because the 40 million announcement didn't happen until this year, 2022.
The 40 million+ announcement was made at CD Project Red's FY21 Investor Relations call on 14 April, which is the same day that above graph was shown. That's why the FY21 sales figures and 40+ million announcement wasn't made until 2022.
The VGChartz figure was up to the end of 2020, so that's why they have it at 1.4 million (which still makes it a million seller, which was my main point).