Q. Is it okay to write “New York Times bestseller” even though the list is called “The New York Times Best Sellers”? The advice in CMOS 8.172 does not really cover this scenario. Thank you!
A. Yes. Unless you’re referring specifically to the title of that list (as it’s styled on the Times website), you can use the name of the publication (New York Times) attributively and treat “bestseller” as an ordinary noun (as you’ve done).
(Note that the entry at Merriam-Webster.com for “bestseller” was updated in 2022 to list the one-word form ahead of two-word “best seller,” an equal variant. References on this site to “best seller” predate that change.)