> On the other hand, MyPy found that only 15% of the 2,678 repositories examined were type-correct Not surprising. In my experience, upgrading or downgrading M

> On the other hand, MyPy found that only 15% of the 2,678 repositories examined were type-correct Not surprising. In my experience, upgrading or downgrading Mypy always breaks type-checking on real code bases: older versions because they fail to infer types or have bugs, and newer versions because they are stricter or error on '# type: ignore' that are now useless (but were needed to work around bugs that are now fixed). And there are 10 Mypy version released over the last 12 months, so projects probably used different versions than the one used by the authors of the paper. While the article does not mention when they downloaded the repositories, I am guessing they started in August 2019, given section 3.1 (with no specified end date, besides the paper's publication in November 2020). And the single Mypy version they tried (0.770) was released in March 2020.