> A rolodex was enough because that's all that could be managed by an individual. If the number of names needed by a person grew past the size of a rolodex, they were simply out of luck because no system existed that would allow them to efficiently handle that much data. That's my takeaway at least.

Yes, absolutely true.

Given "hundreds of filing cabinets" though, how many of those leads can or will even be contacted in the salesperson/company's lifetime? How many leads will themselves have died before you even get to their number?

It's "advancement" only in the sense that we've made hoarding more efficient (which is a technical achievement in itself).