This is something I've submitted feedback back years ago. LM does not track SDT state within the alert itself. So the "in SDT" will report the current state of the SDT when you run the report, not the state of the SDT at the time of the alert. I suggest you also submit feedback on that.
At some point I was thinking about using the API to look at historical SDT and try to match up devices and alerts but never got to that. Since our alerts generate tickets and no tickets during SDT, I believe we just ending up running reports from our ticketing system instead as a imperfect workaround.