It's about as hard to remove a single data point from an LLM as it is to remove a single memory from a human brain.

OpenAI doesn't remove data from the trained models, they filter it at the output level. They also remove it from training data, but of course the model lives on.

I'm a strong supporter of a "do not encode" header / metadata on content that allows individuals, content creators and providers to tell AIs not to encode specific text / images / documents in the first place.