Interesting. This makes it likely that shiitake extract is the type of mushroom used in mushroom seasoning or takii. Most products just say "mushroom powder" and "mushroom extract". Some products list "shiitake powder" and "mushroom extract". I can find no product listing the type of extract used.

Edit: The linked table shows dried shiitake has the highest guanylate and glutamate of the listed mushrooms. Given that the website is about umami generally, this dramatically increases the odds that it is shiitake extract used in said products. It implies that dried shiitake may be the most umami mushroom (though no other dried mushroom is listed).