On the same topic, but a slightly different angle:
When determining the modifiers for the worth of the monster trophy, should you use the modifiers at the time when the monster was killed, or when the trophy was spent? For example, there is a mythos environment card that increases the toughness of cultists - if you already have a stack of cultists in your hand, can you spent them at the new value, or is it only for cultists killed while the environment is in play? My gut feeling is the latter - the worth is based on how difficult the monster was to kill... but this came up in our last game, and I thought I would ask.
At the time you turn them in. So this may or may not be a benefit depending on the value at the time you killed it. But there is no in-game mechanic to keep track.