I have a bunch of duplicates.
I have 2 G10 S30V Leeks, but they have different scales (one set textured and thick, the other polished light and thin) and work well with different styles of dress.
I have 2 each Swamprat RMD and Swamp Warden. They make a good set, one set for me and one either backup or for my wifes use.
I have 5 Mora Craftsmen, a 740, 780 and 3 760's. I bought a 740, 760 and 780 at the same time to see what the Mora thing was about and was so impressed I picked up 2 more 760's (in orange, love that) for kit knives.
I also have 3 carbon steel Opinels, though they're all different sizes.
If you find something good that you like there's no reason not to buy more of the same pattern, especially if you're puting together kits or sets of equipment.