Hard to tell without knowing a little bit about your model and the data.
Could you post a screenshot of your model? And maybe a screenshot of a tablebox showing your count field and the orders?
A sample QVW might help to understand your issue.
Just guessing, but if you are creating the count field in the dimensional table that shows only the 8 customers, a simple Sum(CountField) will return 8. You need to create the field in your fact table if you want to get the order count with a valid customer.