According to Marvin Matyka via. Twitter, the April 15 episode is Riverdale High’s take on the musical Hedwig and the Angry Inch (Chapter Seventy-Four: Wicked Little Town)— and unlike the show’s previous musical episodes, it will feature Cole Sprouse singing. After that, the next episode seems to have been completed as well, since Roberto Aguirre-Sacasa was posting stills from filming in early February.
The next episode (Episode 19) is likely also done, because cast member ädchen Amick (who plays Betty’s mom) posted to her Instagram story on Feb. 19 that it had begun filming. It’s just the remaining schedule that’s a little more up in the air.