If I'm not mistaken, the comparison was made between the uTracer results and results obtained from a different curve tracer, both using the same bogey tube.The reason the uTracer results don't match a bogey tube curve is because such a tube does not exist. The curve is the average of many, perhaps even hundreds or thousands of tubes. Testing multiple tubes on the uTracer shows this very clearly - and the results are quite repeatable over time and instance.
So if they don't match, it is due to differences in how the measurements were taken, not because different tube samples were used.