Marketo Smart List & SFDC Campaign have different totals

Hi guys,

I have a SFDC Campaign (let's call it CAMPAIGN_A) that has exactly 1,000 members.

In Marketo, I created a smart list (in the Lead Database section) with exactly one filter:

Lead: In CAMPAIGN_A

It returns 808 leads.

How could that be possible? There are no other filters / anything associated with the smart list. I've attached a screenshot here.

Help?

Thanks!

Andrew