Project Nemesis is a fan driven website for games that use the One-Roll Engine (like Nemesis, Wild Talents, Reign and Monsters) or Chaosium's Basic Roleplay System (BRP) (like Call of Cthulhu) and the Delta Green setting.
Why might there be paranormal stuff in a green box? Sometimes that is the only fucking thing to do.
You can't send everything to Cell A; Delta Green is an illegal conspiracy, there isn't the funds, facilities, or people to stand around at Mail Boxes Etc. and deal with the crazy shit that comes. The cells are made of competant people who can deal with the shit that comes down. That's why they were picked. The Conspiracy helps where it can, but frankly they are putting out fires 25 hours a day, and they are stretched a little thin.
So, if the current horror has been delayed, stalled, or otherwise temporarily dealt with, you have a giant fucking problem already developing in the next town, and you just need to make do and get going, so that you can show up all fresh in the office Monday morning, with lies of golf games to tell the other guys at the Post Office.
Frankly, most of the time, this works. The Mythos runs on a lot slower clock than human society. A thousand years is nothing to the machinations of the Dweller beyond the veil, but it's god damn forever for an agent. And when it doesn't, well, that's just the way it is sometimes. Sure, it would be great if Delta Green had the money and the manpower to efficiently finish everything; but it turns out that really isn't possible, so pragmatic concerns of the moment dominate the day.