If I used old comments then it's likely that the models will have trained on them. I haven't tested if that makes a difference though.

an unbiased llm shouldn't be producing "style", it should be generating outputs that closely match the training set, as such their introduction should constitute only some biasing toward the average, which also happens in language usage in humans over time. the outcome is likely indistinguishable for large general data sets and large models. i am interested to see how chatbot outputs produce human output bias in generations growing up with them though, that seems likely and will probably be substantial