Step 1 - Check for Null values

1. Create a new calculated field.
2. Using the measure we want to check for available data enter a formula similar to the following: ISNULL( [Measure] )
3. Click OK 

Step 2 - Find Last Date

1. Create a new calculated field.
2. Enter the following formula referencing the above calculation: { FIXED : MAX(IF NOT [Is Sales Null] THEN [Date] END) }

Step 3 - Compare last date against all dates

1. Create a new calculated field.
2. Enter the following formula: [Date] = [Last Date ]
3. Drag this field onto the filters shelf and select True.