grade "A" is not anymore refined than b or c grades. The lighter the syrup the ealier in the spring the sap flowed from the tree. The highest grade is fancy and is very light and thin. There is nothing refined about maple sryup. It is 40 gallons of sap as in flows out of the tree and this is boiled down to 1 gallon to make it thicker.
It is true that the lower grades have more minerals, flavor, are thicker and cost less.
I don't know much, but I am from Vermont so I do know about syrup!
There are probably more minerals in the lower grades due to the photosyntesis. the higher grades are from sap that has been asleep all winter.