The last thing I've done to my b&w images processed as B&W or through Nik is to add one last layer, B&W, to neutralize any color bias that may have come up during processing.
I try to keep my workflow in 16-bit and color so I can keep my options intact but more and more of my work is processed on my iPhone resulting in a jpeg file so to keep things as consistent as I can, the last layer I add will be the B&W layer effects to the top of the editing.
When I've printed a series of images, this fast and easy step has saved the day in making things perfectly color graded when I print on any of my Epson printers.
Hope this helps!