All physically true, but, does it matter? The optimal VTF for any given cartridge is an unknown. We could try to measure by incremental adjustments while taking measurements, but the results would always be a range that is dependent on the accuracy and precision of our measuring devices. Plus the recording being played will also determine the outcome and define the parameters and conditions under which the analysis was performed i.e., the so-called asterisk in the footnote. So, the optimal VTF will always be a range, it can't be anything other than that, and, as long as we are in that range, slight variations of up and down motion on the cartridge imparted by the record and that change the VTF ever so slightly as described above simply won’t matter.
