Well, technically, there was never a 1.3. The repository contains a 1.3 branch, but it is marked as obsolete, and looks to be just a marker to start the development of the "next version". That branch is dated Feb 2010, and the files in the SwinGameSDK are dated Jan 2012. Even if it is a 2.0-dev branch translation, there has been a LOT of development in the last 18 months leading up to the actual 2.0 release, so I don't think it can be considered a good 2.0-compatible translation.

Without looking into it, I think it is, at best, a snapshot of the "latest and greatest" of the dev version of SDL as of 18 months ago, but likely may be just a translation of whatever the obsolete 1.3 tag has in it, which looks to be just a copy of v1.2.14. Note that the latest public version of SDL, 1.2.15, was released pretty much at the same time as those SwinGameSDK files were.