So when they asked my help I told them, you don't have a copyright problem, you have a SEO problem - since people looking for their publications could find them easily online with the stolen copies sometimes appearing higher on SERP than their own. They said they would address that and they somehow came to terms with the fact that the past documents are lost, but they would like to avoid this situation in the future.
I checked some of their publications. They were moderately priced and the content was quite interesting. Many of their customers were very supportive - actually they were sending reports when they noticed the pirated copies. And they weren't saying "Why should I pay for your books when I can get them online?" but rather "Please take care of protecting your content since we want you to survive and publish more books". So, to answer your question, I was very happy to work for them, and I would do it again.
[0] I was told they changed their approach later and started to collaborate with publishers.