Well Aardenburg ID-144 is an Ebony tri-tone that Roark is marketing. What is the point in testing that?
See also #141 in the Aardenburg database, another Eboni full carbon (but as you noted only 3 channel) sample. ID#144 was protected with Premier Print Shield, while ID141 is the same ink set on another paper(HN photo rag) submitted by another AaI&A member, it's now at 160mlux hours in test, and without additional spray overcoat. It is also showing average delta E less than 1. Likewise, take a look at ID# 105. This is Cone Piezotone Sepia tint (piezotone was 4 channel as I recall, now superseded by K6 and K7 formulations), also with delta E less than 1 at 180 MLux hours.
The point of testing all these samples on various papers was that all of them are truly full carbon pigment, no other colored pigments being used. As such, theory said that they should be exceptionally light fast, but theory needed to be proven. Hence, my willingness to test them even if some of them are a little out of the consumer inkjet mainstream market. The test results demonstrate that full carbon pigment ink durability has been proven quite well with these three samples. Now consider ID#146. It is also Cone Sepia K6 (6 channel), but it reached AaI&A Conservation limits at only 6 megalux hours because the choice of media had high OBA content that caused rapid hue shift. Had nothing to do with the robustness of the inks or how many channels were used. Moral of this story is that even a bullet proof "full carbon" ink set will be badly undermined if it's used on a poor choice for media. Hence, the importance of testing materials as a whole system, not just as inks alone or paper alone, etc.
OEM pigmented B&W driver modes are also proving to be quite robust, but definitely not as light fade resistance as full carbon pigmented inks. The problem of course is that not everyone wants a warm tone all the time, and this is where other colored pigments necessarily have to come into the picture (sorry the pun), either by laying down "pure" colored pigments in other printer channels or by blending directly into the monochrome "gray" inks, or both. For example, Cone "Selenium" and "Neutral" are color-blended gray inks, whereas the OEM printer manufacturers' B&W printing modes undoubtedly use some color pigments blended to make their photo gray ink channels but they also allow additional cyan, magenta, and yellow pigments to be laid down by other channels along with the photo grays when using their B&W modes to achieve various cool to warm tints chosen in the printer driver settings.
Bottom line: Pure carbon is the ultimate in stability as Paul indicated, but If you're printing with inkjet and you want dead neutral, near neutral, split tones, or other cooler hues for your B&W imagery you are going to be using a system that involves blended color pigments or dyes one way or another. You won't get to neutral/near neutral with pure carbon pigment, so you will be making some tradeoff for initial image aesthetics versus the ultimate level of ink fade resistance. For most people including myself that choice is perfectly acceptable, particularly when it's done with an informed understanding of the trade-offs.