Looks like the low frequency behaviour of the cartridge/tonearm combination is shaped more by Newton's third law than by the compliance resonance. Modern cartridges (meaning all those built in the last 60 years or so) have too much suspension damping and non-linearity
for the resonances to dominate.
I would stop at this today, leaving conclusions proper until the last post in the series. This is heady stuff, and I fully expect some people to become very upset.
Besides, we are not done yet. So far, we're only studying the motion that is excited by the artificial test signals. What would happen when we expose our combinations to actual real life records? That's the topic for the next post.