The insight I was trying to provide is that buying the list of emails from the list owner probably isn't worth it as it's not comprehensive.

For my methodology, I sorted alphabetically and cross-referenced with our internal deal tracking tools. About 50% of the first 20 firms I checked were missing. I call my scan cursory because I didn't continue after that, and we only invest in a subset of markets and company types.

I see lists like this for sale fairly frequently, and based on what I see it's likely a list of all firms with partner emails that were easy to find.