NR is not normally expected to be applied in raw files. And no, PTP conclusion was that there was correlation between all neighbour pixels, not just left-right.Raw files are never completely raw. NR is applied to every pixel, and the charge readout is measured and converted to a tiff image file in a CR-2 or CR-3 wrapper. You are not seeing direct charge readings from each half of a sensor pixel.
Check this thread till the end: https://www.dpreview.com/forums/thread/4509197