TL;DR
There are leaked strings, NPC textures and maps that refer to both L4D3 and HL3. Some of the data points to day/night cycle in L4D3 and new infected "Nocturnal". One NPC texture is from L4D3, another is from HL3 (according to anonymous source from september). The maps leaked do not work now, might be fixed. One of the maps was test map for HL3 (according to anon source).
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