Gpt3 was trained on completion data so it likely saw lots of raw chess games layed out in whatever standard format moves are listed in, while 3.5 was post train

Gpt3 was trained on completion data so it likely saw lots of raw chess games layed out in whatever standard format moves are listed in, while 3.5 was post trained on instruct data (talking back and forth) which would have needed to explicitly include those chess games as conversational training data for it to retain as much as it would otherwise