I know one developer of sample libraries so far: Embertone
I mentioned audiowatermarking.com above...see their customers list and Embertone among others:
https://audiowatermarking.com/customers
But, heck, Embertone has nice free libraries too, for example
Intimate Strings Lite, it's 15 years old, but still sounds great:

 

This is true. But not only that, I have no idea how anyone would be able to figure out what libraries you even use in final mix, especially when most composers blend multiple libraries together. Look at forums, reddit, YouTube comments, even people who work with samples both professionally or as hobbyists cannot tell what sample libraries other composers are using just by listening to a final mix.
I have not done any research into how these audio watermarks supposedly work (I only know that there was one plugin in FL Studio that allowed you to write or put anything on top of audio histogram) but I highly doubt if these watermarks are subtle that they will be able to survive in a dense mix with many sampled instruments together and be legible enough to work as evidence in court.

My only guess that those companies who claim on their sites that the samples are watermarked only do so to find out which customer leaked the library in attempt to sue them maybe, even though the lawsuit would cost both parties more than 10x the price of the library and if the customer is from another country then most likely you're SOL.

I also doubt that there're people insane enough to watermark a library with tens of thousands of samples with specific identifiable unique watermark for every single customer. It's just a lot of needless work and you would also have to have duplicates of the same library, one exclusive copy for every single customer, that's just a huge waste of storage space. And watermarking that way would be impossible if the library is available for Kontakt Player, since those are encrypted into NI's proprietary format and developers have no access to that. Developers send samples to NI, who then encrypt and release it and that's the final library that every single user gets, everyone will have identical samples.

 

In principle, I agree with you that once a song is finished and released, you don't have to fear being sued.

It's more of a threat from the producers to protect the illegally used samples, etc., from illegal use. That has already worked, which is why the thread starter brought it up. I've posted all these links so everyone can form their own opinion. But what I'm actually missing here is actual proof.
I once asked the AI if anyone has ever been sued for watermarks in music. The AI's answer: none are known.

Quote: Legal consequences could arise if such watermarks are used to prove copyright infringement. For example, a buyer could be prosecuted if their watermarked file is distributed illegally. However, watermarks themselves are not copy protection systems, and removing or tampering with them is not necessarily a crime.

Copyright in the New Music Market with Particular Reference to the Use of Digital Watermarks
Diploma Thesis by Jens Schmelzle | Audiovisual Media Program | Stuttgart Media University | Stuttgart, May 6, 2008
(as PDF in the attachment in German and English)

 

Last edited: Apr 4, 2025

Logically, an audio watermark would only work if you used the sample library as it comes out-of-the-box. As soon as you EQ or saturate you'd be changing the frequency response and balance so they wouldn't match the original.

 

Just for reference
https://surl.li/bzgfil

BFA Vintage Strings Bundle (Kontakt)
License Agreement

The Following End User License Agreement is included with Vintage Strings Bundle. This License is only valid for the individual who has purchased an unopened, new and lawfully made copy of Vintage Strings Bundle from a dealer or distributor authorized by Big Fish Audio.

"The Following End User License Agreement is included with the Vintage Strings Bundle. This License is only valid for the individual who has purchased an unopened, new and lawfully made copy of the Vintage Strings Bundle from a dealer or distributor authorized by Big Fish Audio. "End User License Agreement: The samples contained herein are licensed, not sold to you, the individual end user, by Big Fish Audio. This non-exclusive, non-transferable license is granted only to the individual end user who has purchased an unopened, new and lawfully made copy of this product from a dealer or distributor authorized by Big Fish Audio. All samples remain the property of Big Fish Audio and are licensed only for use in the creation of a live or recorded performance that includes the licensed samples as part of a derivative musical work created by the licensed end user. This license expressly forbids resale, rental, loan, gift or transfer of these samples in any format or via any medium, except as part of a derivative musical work. The samples may not be included, whether unmodified or as part of a derivative work, in any sample library product. Any unlicensed usage will be prosecuted to the maximum extent possible under the law.""