using siri in calendar

I would like to use my iPhone 6 as my main organiser. One of the functions I would like to have available is, to be able to record unplanned events; necessarily these will be recorded after the event. I would like to be able to use Siri for this, but to date, in Calendar at least, this does not appear possible; I have been unable to get Siri to create an event that occurred prior to the current moment. Am I missing something? I have not found any mention of this capability when searching online.

If Calendar/Siri cannot provide this service, I would appreciate suggestions for an app (or combination of apps) that will.