SYNCHRONY

Spare Me
Yes I Can
Nothing if Not
Consider it Done
Hold On
Rather Fetching, Don't You Think?
Of All the Girls to Fall For
No Other Choice
You Wouldn't Understand

Synchrony. Noun, referring to events or occurrences taking place at the same time.

A fitting title for the story that those nine shorts collectively serve as the prequel for. The events of a single Saturday, following the course of several lives as they intersect, intertwine, influence one another - the secret date; the sisters' outing; the three friends in search of adventure; the gentle soul and the conman she works with; the knowledge-seekers and the hidden love they share; the would-be hero and her mysterious 'rival'; the ones watching over them all; and the two runaways searching for meaning and purpose in their young lives.

Those nine shorts are officially known as the SYNCHRONY oneshots, and their sequel is simply Synchrony. They exist in the same continuity as Oathmaker, and indeed occur alongside - synchronously - with it. You can find the continuity's timeline here.

To be more specific, the plot threads in Synchrony are set up by the prequels as follows:
Sunset and Twilight: Of All the Girls to Fall For
Rarity and Applejack: Consider it Done
Rainbow Dash and the Mysterious Mare-Do-Well: Yes I Can; No Other Choice (in part)
The Pie Sisters: Hold On
The Crusaders: Nothing if Not; Consider it Done (briefly)
Fluttershy and Mr. Discord: Spare Me; Rather Fetching, Don't you Think?
Starlight and Sunset, human versions: You Wouldn't Understand