I have a sale date and customer field

 

so far my selection forumula is as follows

 

{salesorders.sdate} < YearToDate

 

Then I have grouped the records by customer and supressed the details. However this only shows me the list of customers with sales that are older than the YTD it doesn't filter out those that have dealt with us within this year, how can I tell it that if the customer apears in the records > and < YTD not to show them?