Here's what I found:
Under Diagnostic Code 5238, spinal stenosis is evaluated using the General Rating Formula for Diseases and Injuries of the Spine. See 38 C.F.R. § 4.71a, Diagnostic Code 5238 (2010). The schedule for rating spine disabilities was changed, effective September 26, 2003, to provide for the evaluation of all spine disabilities under a new General Rating Formula for Diseases and Injuries of the Spine, unless the disability is rated under the Formula for Rating Intervertebral Disc Syndrome Based on Incapacitating Episodes (renumbered as Diagnostic Code 5243).
Source is hyperlinked on the text above. Keep in mind this seems to be a case interpretation and decision which could be outdated, though law firms soliciting their services seem to agree that stenosis is still based on ROM.
I think that the two issues would end up being lumped into the same rating as they seem to be rated under the same criteria. Not sure if you're familiar with the concept of pyramiding, but it's essentially a way to stop people from claiming issues that have multiple origins from stacking percentages on top of eachother for higher benefit. Like if I had a wrist strain, but I also had arthritis in that wrist. I would likely only get the one rating.
Now here's the difference: you can claim nerve issues like radiculopathy and that would be a separate rating.
I'm just a dude going through this process as well, so believe me when I say I'm not a professional this is just my interpretation. I could have been an asshole and just linked the Hill & Ponton site that states it's ROM based but that's a shit answer, it's always better to see it from the VA. Hope the perspective helps somewhat.