Finding first "engagement" date
My guess is there's no good answer to this question, but here's what I'm looking for: I'd like to know the first time a lead actually engaged with our company -- meaning they filled out a form, had some kind of interesting moment, etc.
I don't have any fields set up to record this information, and naturally Last Interesting Moment Date is continuously updated, so that wouldn't be the best solution. Created date might also be misleading, as it's possible they were added via a list upload or something but didn't truly engage.
Is there anything via the API or other tricks to find this data in bulk? Or pretty much only individually via the activity logs?