Now that the Anthropic settlement has received preliminary approval, authors can look up their books in an official tool. From the Anthropic Copyright Settlement site:

To see if your book is included in the settlement, select how you would like to search and enter your search terms.

You can search by ISBN/ASIN, Title, Author, or Publisher.

The search results differ from the search tool The Atlantic created. The site has an FAQ about that:

51. My work was on The Atlantic’s list of LibGen files. Why is it not on the Works List?

The Works List only includes works that meet the Class definition (as identified in FAQ 5). A work on The Atlantic’s list of LibGen files may not meet the Class definition for many reasons […]

Those reasons will disappoint many authors whose work was pirated, but which didn’t meet the criteria for compensation.