Jussi Backman on the Ereignis that wasn't.

[Contributions to Philosophy] can be understood as a contribution to “philosophy,” in the sense of the now-concluded metaphysical tradition, from a standpoint that is no longer contained within this tradition (but is nevertheless rooted in it). Contributions casts a glance at Heidegger’s own transitional situation with a view to an emerging possibility of thinking, namely, articulating Being postmetaphysically as Ereignis. Ereignis is the event or “taking-place” of historical singularity in which meaningfulness “finds its place,” i.e., is contextualized and situated within the There, the “instantaneous place” (Augenblicksstätte) of spatiotemporal situatedness (Zeit-Raum) furnished by the human being as Da-sein. As such a situated place, Da-sein “corresponds to the uniqueness of Be-ing [Seyn] as taking-place [Ereignis].”

In German, Ereignis has a strong connotation of an individual historical event. However, as Heidegger later notes, he uses the word as a singulare tantum, as a noun that is singular by definition. Ereignis no longer refers to single events in their multiplicity, but rather to Being as the singularization of the singular as such. As the parenthesized subtitle of Contributions—Vom Ereignis, “of” or “from taking-place”—emphasizes, Being is no longer approached by way of Dasein as an “exemplary being.” The point of departure is rather Ereignis, the reciprocal correlation between Being and Dasein, itself. However, as Heidegger notes, the preposition “from” also indicates the preliminary nature of Contributions. The fragmentary formulations of Contributions are indications and intimations of Ereignis from a transitional point of view. Contributions is not yet the properly postmetaphysical “work” that could only be called simply Das Ereignis—a work that Heidegger never wrote.

From "The Singularity of Being and the Fourfold in the Later Heidegger".  ¶ 6:03 PM