Complex colors are a specific pigment formula easily thrown off if the base colors vary. If the mix isn't primarys, but complex colors mixed to begin with, now your way off if the primary bases are off.
Variences are just a sign the formula was compromised or approimated. I.e. someone said "who cares it's close" 
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Companies go a long way with color, patents etc. and PR depts. tend to mind them pretty close. E.g. it ain't "medium blue" it's "Ford Blue" or even "Michigan State Police Blue", etc. etc.
