Thanks Marie for your input and advice. I didn't get any examples from Google despite asking for them twice. As you've suggested I'll create a spreadsheet with the list of domains, contacts etc. It's tricky to understand which domain needs to be taken down and which is valid, I don't want to make mistakes and dig a deeper hole for my site if and when it comes out of penalty.
I did get a sitewide manual action so I just hope to get it resolved as quickly as possible. Obviously contacting dozens or hundreds of sites would take some time to complete.