From NNC's own website:

"Subjectivity Of Grading
Limitation of Liability for Grading: All parties understand and agree that the professional opinion required in grading coins involves NNC's subjective judgment. Consequently, National Numismatic Certification, LLC. makes no warranty or representation and shall have no liability whatsoever to the customer for the grade assigned by NNC to any coin."

Seems to me, in my personal opinion, that their opinion is worthless.