Hey Asser,
I will try to make it very simple for you:
If your broker doesn’t synchronize with your time and is changing summer to wintertime, you can do nothing. You can not set in the App from this to this date to be one zone, then from this to this date to be another zone, and do that for 13 years.
If you are with UTC, there will be no changes with winter and summertime, and if your broker synchronizes it with you, you will have the data matched because the DATA IS BARs – open, low, high, and close.
I do not get into these details in the courses because the difference of the backtest is so minimal even though a winter-summer change doesn’t worth the time to do anything about it.
I hope that makes sense.