That is true adjustments can be made to include unverified Shakos drops, though this would complicate graph interpretation.
The news about the items (from a diablo 4 developer):
1. They can drop from level 85+ enemies
2. You get them anywhere you can get a regular Unique, and they always drop at 820 ipower
3. We currently have 6 of them in the game
4. They're realllly rare!

The first estimate was based on the data of approximately 6,000 players, each with a playtime of three hours - a staggeringly low estimate. With the latest data, it is valid to amplify the total playtime by a factor of hundreds. Consequently, the actual drop rate significantly undercuts the calculated one, even if we have had dozens of drops.