Theoretically, continuous distillation can be extremely efficient, as, you're removing as much heat as you're putting into the system. In reality, you get into diminishing returns fairly quickly, because insulation, pumps, heat exchangers, etc, are all far from free, especially at scale.
So the old grading system rated the lighter colored plainer sugars and syrups higher than the darker more flavourful varieties. Since less maple flavour made for a better all-purpose sweetener and a more direct competitor to cane sugar.
Nowadays we usually use maple syrup for the flavour, so the grading system is non-judgemental that way. And the darker grades are more likely what you want.
Correct for things with that specific label, but other X syrup labels can be fair game:
> In the United States, table syrups can be sold under a name consisting of any word followed by the word syrup with the exception of maple, cane, and sorghum. Commonly used names are table syrup, pancake syrup, waffle syrup, and pancake and waffle syrup.[1]