The sample offsets are left up to the vendor - they aren't defined by the API specification.

The sample offsets are left up to the vendor - they aren't defined by the API specification.

That's not totally true...they're vendor specific for most MSAA modes but not for the D3D11_STANDARD_MULTISAMPLE_PATTERN and D3D11_CENTER_MULTISAMPLE_PATTERN quality modes. Those modes have fixed sample locations (the latter setting has all sample locations at the very center of the pixel), and are available in FEATURE_LEVEL_10_1 and higher.

A while back I made a sample that could visualize the sample pattern for an MSAA mode, and spit out the sample locations in XY coordinates, so you could use that to see what they are. You can also query the sample locations programatically in a pixel shader if you're using ps_5_0. I think that last time I checked for my GPU (a 6970) the regular 4x MSAA mode used the same sample locations as the D3D11_STANDARD_MULTISAMPLE_PATTERN mode.