There is something misleading about each of those pie charts, since there should be another two pie charts that shows how many bitcoin are in unknown entities (private hands), so then it would show known entities and unknown entities in order to put the unknown portion into perspective. The pie charts imply that to be the whole bitcoin supply when I would suspect that each of them is depicting less than 25% of the total bitcoin supply.
Good catch and does anyone know on what number these
31% of known BTC holdings
is based on? I did a quick search in the quoted article, but it only talks about 31% of known BTC while not saying how many BTC holdings are known.
JayJuanGee I think your 25% number could be quite accurate. I know it is a guess, but I did the following:

If you look at the table and you go bottom up, you could suspect that most of the 10K BTC - 100K BTC wallets are identified and you can see that when you scroll down on the website and see whether the wallet addresses have a tag. Most of them do. Let's assume that all addresses in the range 10K BTC - 1 mio BTC are known, that makes roughly 3,000,000 BTC.
Then I checked how many wallets in the 1K BTC - 10K BTC are tagged and the number of tagged addresses goes down a lot, but I would suspect it could be around 50% tagged, probably less but let's go with 50%. That makes 2,300,000 BTC.
I then checked addresses in the range of 100 BTC - 1K BTC and there you can see that hardly any address is tagged. I am aware it doesn't mean it is definitely unknown, but going by these estimates based on the tags, it could be around 26%.
In my opinion this makes sense. Any wallet below 1K BTC is most likely not identified. Give or take of course, but the wallets ranging from 10 BTC to 100 BTC won't be in corporate or institutional hands for the most part. Some of them yes, but why would they be identified unless they must be disclosed or have a proven connection to another / bigger wallet of that same entity.
This has been an interesting topic ever since, same thing for how many BTC are lost, but I have found that as soon as you change the source of information, the numbers change too.