I mean it's a BIOS specific feature. Those PCIe adaptors need bifurcation enabled in order to allow the x16 to be divided into 4, 4-lane PCIe NVMe slots. Without the Bifurcation option enabled in BIOS it will only show 1 NVMe storage device despite 4 being slotted. 

 I'm putting a single nvme drive on a pcie x4 card that has a single NVMe port and plugging it into an x4 slot, but that is a good point for others who may be copying me but with slightly different designs. 

 Ahh, I misunderstood. I have an older PC that I put a 16x PCIe NVMe 4 slot in, A 4x is a nice little expansion for an aux PCIe.