Every form submission, in the person's own words, with where they came from. Label each one so tests are judged on good leads, not just more leads.
“Got your name from a neighbour. Can someone come look at patio doors this week? Evenings work best.”
“Can you do a new front door in Medicine Hat?”
The AI labels every lead. “Needs review” means it was unsure, so a person decides; anyone can change any label. The AI reads the answers only, never names, emails or phone numbers.