For Indian Rosewood, this picture gives you an idea of one supplier's grading. Three guitar back sets, from left to right:
Grade 'A' (Second) cost around 38 euros, excluding taxes,
Grade 'AA' (First) 49 euros,
Grade 'AAA' (Special) 71 euros.
If you could make three otherwise identical guitars from these sets, my guess would be that there would be no discernible difference in sound or playability. The difference is largely a visual aesthetic.
Maybe some could be easier for the luthier to work with- I'll leave that for experienced makers to comment on.
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