This is common, there are threads on here that discuss how the right rear tail light harness is actually the "caboose" for the cars electrical system, hence the lower volts. Once you see it you can't unsee it and now when you peruse NSX galleries you'll notice it a lot

. Those that have converted to LED no longer seem to have that issue but it introduces other things you'll need to address (brake warning light indicator, LED load equalizers, modifying relays, etc.).