I'm setting up a smart campaign to set a lead record Acquisition Date for circumstances where this is not set automatically. What would be a reliable trigger for catching the conversion of an anonymous lead to a known lead?
The Acquisition Date is automatically set when an acquisition program is set. You should be triggering leads into programs and setting their appropriate acquisition program. I believe an Acquisition Date cannot be set without it having an acquisition program.
We have cases where it's not set which are discussed here: Setting Acquisition Best Practices
Anonymous to Known is handled in the background. If you have an RCM, it is automatic.