I am currently trying to ascertain the validity of a TPG slabbed note graded GEM UNC 67. The Charlton Catalogue has a top grade of Choice UNC (65)
Why doesn't Charlton go up to UNC 67?
Is UNC 76 an American classification?
My CGPM (31st Ed) just has three levels of UNC listed as "UNC CH UNC & GEM UNC"
My understanding is that "UNC" is a more BCS version of UNC60 & CH UNC would be Unc 63 & 64 & GEM UNC would be Unc 65-70. I understand that on Charlton's preface on "Grading" which starts on page XXii & gives notes on the high ends of Unc on XXiv "GEM UNCIRCULATED -- GEM UNC - GCU65" I interpret as Super gem (67-70) to Gem (65/66).
On the actual Book Value charts I can see no numbers for each & each collector must take the BV as a guide (not gospel). If you encounter a seller who wishes to swear by the Charlton like its the 12 commandments, then perhaps you should shop elsewhere.
'Dean' if you're a 'grade-rarity' collector than I suppose the note in question would be worth a hefty premium to you. How much a premium should be up to you & the seller. If you're not a "top-pop" collector or you feel that the seller isn't very open to negotiating a price, than perhaps you should pass.
Personally, I don't take CCCS as seriously as BCS. I also like going after PMG UNC65 since I find the bidding a lot weaker on these than the 66's or 67's & usually the notes just slightly off centre. To each his own. I have also found over graded notes by Legacy, PCGS & PMG but tbh I have rarely seen much difference between a Gem & super gem (a 65 & 67). I've got a few super gems and I have to look over it with a microscope to see the difference between it and an UNC 64 EPQ.