What type of plot structure allows authors to "come late" to their own story?
The plot structure that allows authors to 'come late' to their own story is in medias res. It is a Latin term which basically means 'into the middle of things.' Sometimes authors don't want to bother giving their characters a backstory, but rather begin the novel in the middle. An example would be Gaiman's 'American Gods,' because we don't see each of the gods' history in the beginning.
A narrative work beginning in medias res (Classical Latin: [ɪn ˈmɛdɪ. aːs ˈreːs], lit. "into the middle of things") opens in the midst of the plot. Often, exposition is bypassed and filled in gradually, through dialogue, flashbacks or description of past events.
In Medias Res means narrating a story from the middle after supposing that the audiences are aware of past events. ... The setting and environment also contribute to add to the details of the action introduced at the beginning of the story.
Hope this helps.
#1: Medias res is the correct answer