they know
As BelArgUSA says - that cardboard was your I-94 and they do eventually cross file them. Still the fact you stayed for 2 plus years and no one bothered to check or come looking for you shows how badly organized they are.
My advice - go the the official CBP websites and see what they say. The German CBP web site has a link to a 900 service you can call for info, on your dime.
I would say get a lawyer but you need to be very careful there. A lot of immigration lawyers are just bottom feeders and many of them are flat out wrong in what they tell you. Buyer beware.
20driver