@Carmelo_DrRaw - thanks! I suspect your interpretations of the CMYK and the RGB are exactly right.
You are exactly right that the gamut warning is good for checking for out of gamut colors in the destination color space with respect to the image colors in the source color space. But LCMS internal soft proofing code has issues with generating correct gamut checks, having to do with things like unbounded and high bit depth linear gamma color spaces.
Marti has indicated that bit depth and “gamma” issues have nothing to do with soft proofing to a printer profile from a perceptually uniform color space. And of course this is true by definition. But again, that stance doesn’t solve the user problem of making accurate gamut checks to use when making editing decisions and decisions about output RGB color spaces (whether for display or for further editing in another image editor).
This is one reason why I’ve been asking what the source color space for soft proofing really is in RT. Apparently it’s CIELAB, in which case hopefully the “linear gamma issues” associated with LCMS soft proofing won’t come into play.
In any event, your soft proofing code also seems to generate better gamut checks than LCMS gamut checks. I say “seems” but I mean “does”, at least for all the cases that I’ve checked.