I'm not sure. I think it's not so much the quantity as much as it is the quality. After about 50 thousand or so ranked messages, I can train myself to some extent. But, if those 50 thousand messages are mediocre, I can only train myself to be more mediocre.

Of course, machine learning is a dark art, so I can't say for sure.
spam fails_task lang_mismatch pii not_appropriate hate_speech sexual_content quality toxicity humor helpfulness creativity violence