Why does OS not change time twice on daylight savings time rollback

My system has correct timezone file and am sure it will change time from 2AM to 1AM on Nov 3.
But why does system not change twice when the clock reaches 2AM after first change? Is there any flag or hardware clock is compared?

I tested DST rollback multiple times, OS changes time to 1AM whenever. So, when the time changes on Nov 3, how can OS stop changing time?

zdump -v | grep 2019 shows zone info changes from CDT to CST, and gmfoff is different.

I am cursious how OS recognizes manual change and real change..