Once the new letters have been created you will need to select which absence codes will count towards each letter.
From Reports menu, select Attendance Letters to Parents.
Select the new Letter that was just created at the top of the form, in this case the letter is SARB. Notice on the right under Attendance Codes to Count that only Absence codes are checked. This coincides with the Default to Absence Codes option selected when creating the letters. Check or uncheck any code that will apply for the selected letter. An All and a None button is also available to assist with code selection. Codes selected will apply to All parts of the selected letter.