Anything with one of these:
Fellowship:
Shadow:
Maneuver:
Archery:
Assignment:
Skirmish:
Regroup:
does not stack effects. However, cards that say something like, "While you can spot an Uruk-Hai, the Fellowship archery total is -1" does stack.
I realized the confusion now. I did say 'stack them,' but I meant "load the deck with them."
-wtk