When I worked for an aerospace company that had been recently taken over by an American company they called for a meeting at a set hour via a newly installed email-come-appoinment app.

So in the last week of March some people turned up to find most had not because they had been reminded verbally. The DST date in America is different to the UK. The app coped with the longtitudinal tie difference but was tied to the American DST dates.

My cousin's husband told me that in Canada, where he traveled as a salesman, that there were farming communities that didn't have DST that surrounded towns that did (in the 60s). Or maybe it was Double versus Singe ST. And they had exclaves of nearby timezones for financial reasons. He said it was very complex.

In the UK we call it BST (British) because we had Double Summer Time during the WW2