This shit has been happening for far far longer than cheeto. It's bipartisan military organization incompetence, and the exact issue that allowed the Snowden leaks to occur.

The markings tell people with clearance how to handle the documents more than anything else. You have no way of knowing if it's a legit marking.

Obligatory, I am not a lawyer.

If random citizen finds it on the street they can't be punished for having it. But the government can repossess the document at any time.