What counts as a collectible Shell
Count a Shell only when it becomes a persistent playable option. This prevents the common mistake of mixing Harros from the prologue into the eight-target checklist.
Route planning
Pair Shell routes with nearby weapons and map fragments. Note the boss or quest item prerequisite beside each name, and return to Marrow Keep when an unlock chain requires a memory interaction.
Before New Game Plus
Use the late-game free-exploration window to compare your inventory against the checklist before starting another cycle.