It seems VTA/SRA have the most deviations of all geometric and mechanical tolerances and standards. For many years, there was a 5 degree difference in VMA between US and Europe.
On the good side, VTA doesn't have at all as big impact as zenith and azimuth for several reasons; the amplitudes for vertical modulation is never as high, the most important audio (voices, soloists) is normally centered (i.e. no vertical modulation) and normally bass below 100Hz is summed in a stereomix.
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Sorry, can you explain how you do for example a zenith adjustment with your ears?
In my experience, you may hear the error, but you see it on a scope long before you can pinpoint what the error is. Usually it's never just one error but at least 4-5 combined errors.
To know how to individually adjust 4-5 parameters on a cartridge just by hearing must very hard, not to say impossible.