Broadly speaking, there are two K1 versions. The early one, which was produced until early 2020, and the late version, what we generally call the "2020" or "post-2020 version"; we don't use it officially but MK1 and MK2, if there are only two versions, would be correct. The major change that occurred in 2020 is related to the new barrel, which is unchoked and designed to fit perfectly with the K1 that fires directly from the magazine, and now can shoot accurately both pellets and slugs. The latest K1 also performs very well at any power level, while the original version performed considerably better at high-power ones.Other than that Huben is a manufacturer which constantly improves quality control and listens to its customer’s feedback to improve its platform. That means that there might be slight differences between each batch, adding incremental improvements and better overall quality.Any other labeling is the product of users, YouTubers, and/or reviewers, however, it is not officially endorsed, as they only reflect these minor changes which do not make for stark changes in parts and/or functionality.