This is a question best answered by people like @wolf because I can only speculate. If the camera colour space got mapped just once to the working space at the beginning of the imaging pipeline (without some further re-mapping), and if the relative colorimetric rendering was used for the mapping, then PhotoLab would re-map the out-of-AdobeRGB colours so that in effect there were no colour subtleties preserved for those initially out-of-gamut colours.
Well I can see subtle differences for some colours outside of Adobe RGB on my pretty old wide gamut monitor (esp.in the yellow/red range).