Both GPT-3 and GPT-4 mark this date as their 'knowledge cutoff date'. Maybe this date is chosen on purpose, in order to avoid a negative feedback loop, where the learning process of their own LLM is influenced by the output of bots that are powered by their own engines?A public reminder: September 1993 was the old 'eternal September', where the big collaborative message board of olden times died, due to a sudden influx of new users. See: https://en.wikipedia.org/wiki/Eternal_September