They can't make something retroactively illegal, but piracy is already illegal. They'd just be retroactively making it harder to get away with. Much like how we

They can't make something retroactively illegal, but piracy is already illegal. They'd just be retroactively making it harder to get away with. Much like how we've used forensic evidence to put people in jail years later, even if our forensic techniques didn't exist yet at the time of the crime.