@Greg I never realized how complex the whole thing is until I worked for an operating system vendor.
Most devs can just ask the OS and get a reliable answer about DST. It's a pain, but there are libraries and data files shipped with the OS.
The reality is that some countries change when DST is on a yearly basis, and some not until it is very close to the switch over. The dates depend on who is in power politically (and which holidays they care to avoid).
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