The serial numbers on the back are actually the US Patent numbers. These are the same on nearly all Miller/Gougler/Miller padlocks.
I don’t have any information on code number 4018.
In many cases where a large group was manufactured for a big customer (schools, factories), the factory seems to have used code numbers unique to that order. A code book was sent to the customer and the ordinary codes simply do not apply. That might be the case here.