Good catch on the graph - didn't see that on my phone's screen.
I agree about the impedance; very nasty dip. I am surprised to see that. I wonder if Dennis would weigh in since it supposedly uses his crossover. I imagine something was wrong with that speaker, as that design has been around for a while and I don't recall anyone saying it bottomed out at 75dB. That particular speaker might have been flawed in some way.