Sorry guys, if I ask for this, but make me understand: from posts seems to be available a fixed non official 8.1 update for Ativ S, right?
Why Samsung didn't put it on regular Update screen?
What are CSC, ATO and other acronyms? How can I know what I have?
Well, if you did followed this thread, so far you would know the answers to all of this questions you have, cuz each was answered numerous times in this thread. So, since i don't want to be criticized from someones here for telling people to actually first read then ask questions, i will answer you
What we are talking in the last 6-7 pages is OFFICIAL Samsung firmware for WP8.1.1, but for unknown reasons only the phones having or running on ATO CSC are getting it, so this is actually kind of a workaround. This is official firmware (update) since it's going over OTA (Over The Air), and that can be released ONLY from Samsung.
On your question Why Samsung didn't put this on regular Update Screen ... Well, so far from what i know Samsung was never telling the news that they have new firmware, they just roll the update out. It's not like on Nokias.
But if you mean by that also why is not this on Update Screen on the phone, that's because like i said above, only phones with ATO CSC are getting it by now. So what you read here is people try to flash ATO CSC on their phones so they can be able to get the newest Samsung firmware 8.1.1. People who already run on ATO or have ATO in their CSC list, doesn't have to do nothing, they can only switch to ATO and they'll get the firmware.
Mind that this is NOT a firmware for people running Windows Phone 8.1.1 Preview for Developers. People with that usually downgrade to WP8 GDR1, 2 or 3 and then get the official Samsung 8.1.1 firmware.
CSC or short for Country Specific Code, where ATO, NEE, DBT, etc are names of the country specific code.
Hope that clears you a bit, for other things just use Google, it's very easy