"Taint" requires that the code is demonstratably derivative from the *GPL licensed work.

This is actually harder standard than some people think.

The absolute clean room approaches in USA are there because they help short circuit a long lawsuit where a bigger corp can drag forever until you're broken.

It's harder than some people think, but the author does a lot of the work when he names the resulting artifact "chardet v7.0.0". If I thought I was writing the kind of arms-length reimplementation that's required, I would never put it into the versioning scheme of the original, come on.