I pinged Mooch, his response to my thoughts of the number of contacts along with the type of material of them having a difference
"I agree. The difference in resistance for all the different materials except SS is tiny though, microhms, and there won’t be any voltage drop differences in the tubes themselves. But you are definitely right about the other stuff! The voltage drop differences due to the contact patch size of the contacts, the contact patch size and pressure levels in the threads, and the lack (or presence of) of oxidation layers can have a huge effect...hundreds of time larger than the voltage drop in the metal itself. "