A Smart Campaign with a Data Value Change trigger for a specific field does not pull in newly created leads, even though the leads have the specified value in the field.
Marketo does not log Data Value Change activities for fields that are populated in the creation of a lead. If the value changes after the lead is created, we log the Data Value Change which would then trigger the appropriate campaign.
If you want to include newly created leads along with existing leads in your campaign:
Add a "Lead is Created/Person is Created" trigger to the campaign along with the Data Value Change trigger
Add a filter for the specific field and the desired value.
This will allow the campaign to fire for both new and existing leads.