The Set 4 Shadow Card's effect starts as "You may have more than three copies of this card in your deck."

In this situation, my question is whether or not this also expands to the Shadow Cards from the first set, which aside from the deck amount and one POW, is the same card.

I'm in a small race to get a Shadow Deck with another player who is working on a Dusk deck, so I'd appreciate any information before I decide how much I need to spend on Set 4 cards.

it actually does not expand any of the old card to the new ruling so only the 4th set will be able to have and unlimited amount of shadows in your deck but since it does not say you can have more than one on the field at once i'm not sure if you can play them at once. thats only if you are using them as friend cards. and because the new cards have the new homeworld icon the old sets are missing a big part of the game such as the new Hundred Acer Woods says that all HAW friends get something extra (cant remember exactly), and since there are no new HAW friends it does nothing right now unless you have some japanese cards.