If it is a Model B, then your reference to 50,000 is understandable as nearly 45,000 engine/transmission assemblies were manufactured before the first of those was installed in a passenger car as a result of the decision to defer Job #1 until a production version of the V8 engine was available.
There is ample evidence that those warehoused Model B and BB engine transmission assemblies did not come out of storage on a first-in, first-out basis. Hence early B chassis and early body, but not necessarily a low engine number. It is only the V8s where low engine numbers inevitably show up in early chassis and body configurations.