Before my successful (pre-fogged) safelight tests I fired up the Duplex, let it warm for ~30 minutes, then looked at the CD reflections unfiltered. In addition to the massive yellow sodium doublet, I saw the much, much fainter blue and green spikes. I also saw the extra deep red spike.
Then while looking directly at those spikes I interposed a single layer of #19 filter. The blue and green spikes disappeared. When I removed the #19, they returned. Back and forth.
Later, when I performed the safelight test I was able to leave a sheet of Kentmere Bromide #3 graded paper out for ~30 minutes with no hint of fogging.* As you may know, bromide papers are very fast. It should have responded to any blue light present. But it didn't. It remained pure white. (Even checked with a reflection densitometer to factor out my subjective eyes.)
So as I said, I too am confused.
Also keep in mind that if you use a cover sheet of Rubylith you will likely be filtering out all of the yellow sodium light as well. At least in a perfect world. I've never tried it myself, so I don't know how much will pass. Maybe only that secondary red spike I mentioned above?
* Apologies, as I earlier identified the test paper as Ilford MGIV. It was actually the Kentmere Bromide. The Ilford was used for my red LED safelight testing.