You also need to start playing before Step 2, either loading a save in Step 1 or starting a new game. You can't load a save that's already in Step 2, otherwise you'll miss the chance to choose your relationship standing with Derek and won't be able to play his Moments.
You do need to play Derek's version of the Soiree to get Derek's Step 4 epilogue, you can't do Cove's version. But that doesn't unlock his other Step 2 Moments. There's a yellow button on the right side of the Moment screen. You click that to switch over to Derek's Moments.
