Unfortunately, that often doesn’t include the ultrasonic range, nonlinear distortion, or a bunch of esoteric stuff that people clearly are able to hear directly or the secondary effects of, sometimes more than the usual specs, but for which you need a real expert and some high-end gear to detect. NWAVGUY, who designed the O2 headphone amp and ODAC, and did many gear tests before disappearing from the audiophile headphone scene, demonstrated this quite a bit.
I was surprised Rightmark even detected the IMD, let alone grouped it into at least some of its total harmonic distortion figures. I first assumed it was in error, but was able to confirm it with other methods like the spectrum analyzer in SoundForge when not using any conversions. Then other people verified it with their own tests. You do certain simple harmonic distortion tests and the players’ numeric results come out as clean as the InMusic specs, though clearly their original frequency specs were in error, like Engine OS is converting to a lower sample rate than the track you play.
So, it’s certainly possible a mixer can do weird things and True RTA & Rightmark wouldn’t show anything significant, as they’re not even professional grade tools and have flaws. Most of the people I’ve seen using any real pro testing gear on DJ equipment barely even scratch the surface on the tests they could be running. And that’s not getting into the people using consumer tools who don’t know what they’re doing or don’t bother to double and triple check with other methods.