Another idea, which has possibly been discussed by the Refs, an NPC bank.
I basically see two types of NPCs, ones that are specifically tied to a character, and more general ones.
In Barnum's Halloween adventure, Raindancer's parents have been discribed, so the Ref can help in running them. That description (and perhaps Ref notes on anything that happens with the NPCs that might be important in the future) might be best put in Raindancer's character thread.
But more generall NPCs, like say a police officer some characters interact with, it might be good to have a general NPC thread for them, creating a "bank" of NPCs that can be generally used by Refs.
Now, clearly Refs will NPCs that they want to maintain more control over, those would just be left out of the "bank."