According to the Microsoft documentation, Windows only supports a single set of "current timezone translation parameters" that are in effect from the Big Bang to the Last Whimper. What it does support is a "current" and a "future" set of data defined by the "year". This permits updates to "next years" timezone settings without having to reboot the computer (pffft). However, the timezone setting applicable to the "current year" are used for all translations from the Big Bang to the Last Whimper. As I said, Windows is highly inconsistent. Not even Microsoft can figure out how it works, and they supposedly wrote the bloody thing (it cannot be IBM -- OS/2 prior to the "great renaming" when OS/2 got poached by Microsoft and renamed "OS/2 New Technology" and then just "Windows NT" -- used the complete IANA database. Since that code was written by IBM presumably Microsoft had to re-write it as part of the "Great-X-ing" (DirectX, ActiveX, X this and X that, which was really removing IBM patented technology to which Microsoft had no rights with home-grown replacements) and they did not know how to handle timezones (what, being a little bitty company that only existed in one wee city and only did business from their lemonade stand).