Does "Last 30 days" include today or not?

You're not double counting. Last 30 days ends yesterday, and Today is separate. The reason it works that way: today is always incomplete and still moving, so including it in a 30 day total means the total changes every time you refresh and is never comparable to the 30 days before it. Ending yesterday gives you 30 whole days that can be compared against the previous 30. So if you want to say both in one sentence, "X over the last 30 days, plus Y so far today" is accurate. Worth knowing for the same reason: if you pick a custom range that ends today, that last day will be partial and will keep growing. Nothing is wrong when that happens, but it does make the last bar on a chart look like a collapse.

That explains the cliff at the end of my chart that I have been quietly worrying about for a month.