A few ideas:
1. Try leaving the screen and returning. For example, if your list is under the LeadsDatabase tab, try switching to Marketing Acitvities, then back to LeadsDatabase. Sometimes the Marketo screen is presenting old information and you have to leave to get it to refresh--a simple screen refresh via the browser won't work.
2. Make sure you're not checking too soon. It takes a while for a 7000 name list to upload into Marketo. If you check the Smartlist immedeately after you initiated the load, only 50 may have been processed by the time you looked.
2. Try looking at some of the leads you think should be showing up but aren't. Make sure you've really got your "IsCurrentCustomer" set to what you think its set to.