Doesn't that chart say that only port 4 is available? 6 and 7 are not handled by the Intel chipset so they are always available.
I'm looking at the RAID mode chart for M2D_32G M.2 connector, PCIe x4 SSD because the Samsung 950 Pros are not SATA, they are PCIe 3.0 x4 NVMe. There's an "x" (meaning not supported) at position SATA3_0, 1, 2, 3, 5. But that doesn't explain why port 5 is working for you... Even if you look at the non-RAID mode chart for M2D_32G M.2 connector, PCIE x4 SSD, then it shows port 4 and 5 are available.