What is the past counterpart for "scenario"

Despite what Wikipedia may tell you, there is nothing preventing you from using scenario to refer to past events, especially if the actual circumstances are unknown or unclear: From NOAD:

scenario |səˈne(ə)rēˌō; -ˈnär-| noun ( pl. -os)
a written outline of a movie, novel, or stage work giving details of the plot and individual scenes : imagine the scenarios for four short stories.
• a postulated sequence or development of events : a possible scenario is that he was attacked after opening the front door.
• a setting, in particular for a work of art or literature : the scenario is World War II.

Note that the last two example usages concern themselves with past events.

Addendum

The Wikipedia link you reference no longer contains any prescriptive notion such as you mention. It does, however, say the following:

Surviving scenarios from the Renaissance contain little other than character names, brief descriptions of action, and references to specific lazzi with no further explanation.

This is clearly a use of scenario in the context of the past.