It should also be noted that there was not one "Tank" SN used, as each component had its own set of serial numbers to be analyzed. In this specific example they used gearbox SN's along with chassis and engine SN to provide the estimate.

These statistical estimations were cross-checked with a broad range of other sources, in an attempt to gather data on everything from the number of tanks produced, to the number of factories in use and a variety of supply chain factors.