I beleive the logic is that you can buy the three boxes without the need to buy the core, therein making the location cards useful. Maybe.

I thought the duplicated location cards are for easy reference. Because I have the problem, that if the location card is lying face up on the table, I can't read the rules text. But now I can put one card on the table for character stand-ups to place upon or beside them, and still have another card in hand to read the location's effects. Of course these effects are also printed in the GM Guide, but I find it handier to have them on cards ....

my 2 cents:

I think multiple location cards in play is to make abstract combat interesting and tactical. Placing upwards of three location cards on the table makes abstract movement meaningful. The key is to place them close enough distance from each other, so players will actually move to them to gain the tactical advantage of the card without feeling the fatigue cost is too high. Then your combats may move easily from street -> roof top -> street -> beer garden just so your player with the drunken trait actions can get them in play

Crazy Aido said:

If I remember correctly the core box did not contain duplicates did it? The GM vault, in itself, contains duplicates. So for me that means that I have three copies of 12 locations. But those that "only" get the vault-boxes get duplicates of the locations right out of the GM-box.

The idea of the GM using them to reference is a good one, at least it makes some sense.
Daedalum's idea, to make abstract combat more interesting and tactical is good, but I don't know when I'll be using two forges at the same time. Plus there are only 12 locations that you can do this with, and most of them are kind of specific (like wizard's tower, wood elf cairn etc.).

Still, I'm happy I got the GM vault. I've got to have everything eventually right?