Well, Bob, that is what is published in the Production Register for the Unstyled "B". And that Production Register lists dozens of model "B" tractors where the "ship date" precedes the "build date".
For example, S/N 31842 has a "build date" of 1937 01 18, but has a "ship date" of 1937 01 16, as does 31850, 31857, 31858, and 31862. So what's the deal with "shipping" a tractor two days before it was "built"??
There have been published explanations in Two-Cylinder that "build dates" are not necessarily the actual date of completed manufacture of a tractor, but the date a tractor was entered into inventory in the warehouse.
There may also have been accounting games played regarding inventory quantities and inventory tax liabilities that required "adjustments" in published dates - or maybe there were a lot of recording or transcribing errors made by the time Two-Cylinder published the Production Register.
At any rate, that's the information that's available and published. And in cases like this, it seems to raise more questions than answers...