ATIS is updated on a schedule, not continuously. If you are on the ground or approaching the aerodrome for more than 30 minutes, you should re-monitor ATIS before contacting the controller again. If the identification letter has changed, it means the information has been updated—typically due to a weather change. In that case, you acknowledge the new letter when you next transmit.

If you arrive at an aerodrome and ATIS still shows the same letter (e.g., "Information A"), the information has not changed since you first heard it. You may use the same letter in your next transmission.