I was just at a high end body shop yesterday, and they talked about this. They carry 3 different brands, and use that flexibility to do the best matches possible. Biggest problem is when an OEM was painted with solvent paint, and now only water based is available.
Through years of experience they have developed a system that works out well for them. They paint a piece of metal or plastic with the code provided. That piece has a large round hole in it. They hold up the painted piece, and look at it against the car, under different lights and angles. They often need to tweak the color or metallic to get the best possible match or blend. They said that often times the clear coat has as much to do with the match as the base paint. Even different primers will give different results. The temperature or humidity, of the paint booth with also effect the match. nThe paint sprayer used, the thinning of the viscosity, the air pressure. Sounded like a Rubics cube of variables.
The human element also comes into play. One owner will be happy with the match, while another will find it totally unacceptable.
If you are fussy, it pays to hunt around for the best painter you can find, and let him work his magic.