Saved Search That Displays All Customers That Were Not Invoiced Last Month

1. Navigate to Lists > Search > Saved Searches > New > Customers.

2. On the Criteria tab > Standard sub-tab, enter a filter for 
Transaction : Type = is Invoice

3. On the Criteria tab > Summary sub-tab, enter the following criteria:

Field = Transaction : Date
Summary Type = Maximum
Description = is before start of last month

4.  Click the Results tab and set the following fields: 

Field = Name
Summary Type = Group
Transaction : Date = Maximum  

5.  Preview or Save