This should always be the first explanation when you're speculating about something involving ChatGPT or Bing Sydney, if you aren't directly using the API and comparing temp=0 responses to identical canned prompts. There are lots of smaller models & filters and prompts involved, all of which are much easier to update than the behemoth underneath, and which do get updated frequently without notice. People jump the gun constantly on assuming it's the biggest model which changed.