There simply is no proper way for doing that without using some database which also needs frequent updates.

Some countries change the switch days every year using a couple of dice to specify them.

For a proper implementation such a database would be required. Also someone maintaining it.

SetClockNTP just knows a bunch of countries which are switching time on fixed dates. e.g. last sunday in october.

So it simply takes time zone information from locale and the matching GMT together with a build in list of rules for the day time switches. It has no proper and fully featured implementation as that would require the mentioned database containing up to date information, which would be a job for locale.library itself.