Hello.

This may be a stupid question, but:

What are the rules regarding usage of Aragorn (Leadership) and Aragorn (Lore) in the same game?
Also, what about Gandalf (Core) and Gandalf (Over Hill and Under Hill)?

Thanks.

you described 2 different scenarios

you can have 6 gandals in your deck, but only 1 can be on the table at a time

you have the manual? bottom left corner of page 8

You can still only have 3 Gandalfs in your deck. From the manual, page 9:

"No more than three copies of any ally, attachment, or event card, by title, can be included in a player’s deck." Even though the two versions of Gandalf have different art, they share the same title, so you cannot include more than 3 copies, combined total. The same goes for other uniques (Bofur has a Spirit and a Tactics version).

And yeah, you can only have 1 card on the table with a given title, if that card is considered "unique." That includes heroes, so you can only have one copy of Aragorn in play even though 2 versions are available.