Dispatch - Lists show 0 Contacts

I created a list in Sendgrid and then populated the list in Dispatch using a SF campaign.  The list shows 0 Contacts, both in Dispatch and in Sendgrid. I encountered this before with another list, and the number of Contacts was updated only after I sent an email to the list.  How can I get the list count to update before I send an email so that I'm sure how many recipients will receive the email?