is the 项链 blair wears in 4x02 the same as the one Chuck gave her in 3x18?

I think the 项链 is different...

Nope it's not the same, but they do look similar from that screenshot 你 got from 4x02. The 项链 in 3x18 was from Cartier, but the one from 4x02 was from Harry Winston.