Every time the ATIS is updated, then the letter is changed. The pilot then reads back the letter they heard to the Air traffic controller to verify that they have the latest information :) There is no order. It’s basically a two way verification for the pilot and controller. The code is randomly generated if I’m not mistaken.
Notice the: “Advise you have information sierra”. When contacting a controller, you would advise them that you have information sierra, which would mean you are aware of the current weather conditions or any NOTAMS. In this case, you would be letting the controller know that you are aware of the 3000 ft ceiling and that the ILS for 01R is out of use.
Information Zulu would be the most recent if they’re on hour 26 of the cycle. It all depends. It could be Information Zulu, Alpha, Golf, November, or any other letter. The letter of the cycle is dependant on the hour of the cycle, just like time. Hour 5 of the day is 5am, Hour 5 of the ATIS is Echo. Same concept, just letters instead of numbers.
I have no idea. I usually ask the captain something whenever I’m on a flight (every couple weeks or so), and I didn’t ask him that question. Maybe there’s differences between Transport Canada and the FAA when it comes to ATIS messages? Again I don’t know. Constructive feedback and maybe correcting me would be more useful than just telling me I’m “wrong”. I feel my information is pretty reliable considering I got it from someone who’s paid to know this stuff, but feel free to correct me if you’re an expert in the field. I’m not a pilot, I only know what I’m told.