They support Geforce 600 and up. I don't even think Nvidia released a Geforce 800 except on mobile which is just a rebranded Geforce 700 so it's likely actually supported.

on my laptop:

$ lspci | grep -i nvidia 03:00.0 3D controller: NVIDIA Corporation GM108M [GeForce 840M] (rev a2)

Note the 'M' at the end of the model number. The laptop GeForce models are different (and less powerful) than the desktop models. According to the website, the 840M supports "entry-level gaming", which isn't really the primary use case for Vulkan.

Here's a full list of conformant products:

https://www.khronos.org/conformance/adopters/conformant-prod...

I don't know why some dates are in the future..

They want you to buy new hardware ;)