I am certainly no paint expert, but I think you might have the answer to your own question there.
The reason there is variance in the paint color for any given paint code is that each paint company has their own 'recipe'. In other words, a color like my Hemi Orange is made up of 'x' units of red, plus 'y' units of yellow, plus 'z' units of some metallic base. Sort of like the earlier comment about Home Depot paint mixing, you know? So my Sikkens EV2 looks a little different than Dupont EV2. That situation happens today with solvent based paints.
I would guess that the color matching is a result of computer color analysis, not a result of a bunch of lab time or anything. They already know the 'recipe' for their base colors, and they work from there. I don't see the analogy to sheetmetal, which involves developing new tooling and such. But we certainly all know the current paints, and if using them puts your mind at ease, then that is priceless!
-Tom