Here's an explanation about the grading standards and sugar content of maple syrup. This is also part of the organic certification process:
Since taste is such a subjective thing maple syrup is graded strictly by color. The grade kit I use is a LoviBond Maple Grading kit. It is the only grading kit that is USDA approved. There are other grading kits available which are much cheaper. However these kits are temporary and over time the colors will change. They are meant to be used for one season and then discarded. I've seen in some sugar houses kits that are 20 years old and still being used. That's why our syrup as far as grade (color) will be always the same.
If someone doesn't use a grade kit at all and bottles their syrup, they can grade the syrup either dark or extra dark or in Vermont grade B. As long as you grade the syrup darker than it really is it is legal. What that means is a lot of producers and most bottlers will have their labels printed Dark. However sometimes it might be Medium, Light, or Dark grade that is in the bottle or jug. So what happens is the consumer could be confused thinking the syrup they have been buying is always different.
There is one more thing to add about the grading and this really applies to the large bottlers. This also explains such a variation in taste. Simple put-- they will take and mix the different grades of syrup to obtain whatever grade (color) they are bottling at that time. So every time they bottle there will be a great variation in taste. The color might be the same but the taste will always be different. ALWAYS! As part of my organic certification I NEVER blend to make a grade.