If you have 2 leakers they can just run a tool to compare the difference between the file and spot any watermarks. Of course the next level is making the waterm

If you have 2 leakers they can just run a tool to compare the difference between the file and spot any watermarks. Of course the next level is making the watermark so there is a bit that is unique to 2 users only so you will then know the exact 2 who leaked it.