Some Marketo records have a discrepancy between the date of the New Lead activity in the Activity Log and the Created datetime in the lead record.
What you have noticed here is the difference between anonymous and known record creation.
In Marketo Smart Lists, there are 2 filters:
- Lead Was Created
- Created At
"Created At" is when the anonymous record was originally created in Marketo.
"Lead was created" is when this anonymous record was 'created' as a Known Lead in your database.