I don't know what guides you've been reading, but a prefix of NT is never, ever valid. No matter how nice the leather seems, a real Coach would never have that prefix. The numbers/letters before the dash indicate the month, year and place of production on a bag made after 1994. Prior to that date, serial numbers were unique and all numbers. In a creed that has any letters at all, the first digit has to be a letter of the alphabet, between A and M, and the second digit has to be a number. Fakes often have hardware stamped "solid brass." Coach only used solid brass hardware on some bags made in the 70s and 80s, and a few styles made in the 90s. You will hardly ever find a bag with both a letter in the creed and solid brass hardware.
These are the only guides we know of that contain accurate information.
http://search.reviews.ebay.com/members/salearea_W0QQcpnameZmembersQQprZsaleareaQQuqtZg