Clear only when age is not known

app/models/derived_variables/sales_log_variables.rb

@@ -160,7 +160,7 @@ private
     (start_index..6).each do |idx|
       if age_under_16?(idx)
         self["ecstat#{idx}"] = 9
-      elsif self["ecstat#{idx}"] == 9
+      elsif self["ecstat#{idx}"] == 9 && self["age#{idx}_known"] == 0
         self["ecstat#{idx}"] = nil
       end
     end