Council of Elrond

Play this card on your avatar if he is in play. If on your avatar, one of the following cards is worth full (if worth any; then place this card with it for 1 ): Clean the Greenwood, ... Cannot be duplicated for each of the above named cards.

I understand that you can't play two of this card on the same copy of a resource, but if you have two separate Tower Raided in play, for instance, could you place one Great Achievement on each copy Tower Raided?

I'd say no but this is based on gut feeling.
I'd say you could e.g. have one on tower raided and one on the great greenwood.

I am curious to hear Eric/Nico's answer.

You are (both) correct.
It "cannot be duplicated FOR each of the above named resources", so this refers to the whole set of cards as mentioned on Great Achievement, e.g. all Tower Raided in play. So if your opponent manages Great Achievement on Tower Raided first, then tough cookie!

Otherwise it would have said "cannot be duplicated ON one of the above named resources", making the target an individual card.

Wow, that's really interesting. I didn't notice that it doesn't have the duplicated "by a given player" line. Thanks for the clarification!