How to Build a Contact List from a Company List: A Comprehensive Guide

I built a great company list and now want to find contacts at those companies matching several criteria. I tried to run that with a LinkedIn enrichment but only got results for 18 of 2.5K companies, which I know if vastly lower than reality. But I think it’s because I don’t really understand how to build a contact list from an account list. Is there a resource or guide on how to do that?