Why 66 to 99? This makes even less sense than the 1-70 system.
Also, how do you make a distinction between "A note that has not been released into general circulation" (99-96) and "A note that has been released into general circulation." (95-91)? Even unc notes have been realeased into circulation if you think about it. It "circulated" from the printing company to the BofC to some branch of some bank to a teller, then to a collector, then to another collector, and so on, even if it's perfectly preserved as a gem unc note.
This is already a huge source of confusion in the current system where some unknowledgeable sellers list their notes as "uncirculated" based on their assumption that the note has not been out in circulation (whatever that means??) even though this really has nothing to do with the grade of the note which could easily be anything between VF(or lower!!) and Unc, even if the note was originally obtained directly from B of C.
Other than the added flaw of the meaningless distinction between "Uncirculated" and "Circulated" that is made, this system is nothing but the good old Unc, AU, EF... system we're all familliar with but with the intuitive labels replaced by arbitrary numbers.