The scanner does show the NAC in hex. On trunked systems, the site's NAC is usually a subset of the SystemID. In Michigan, on the MPSCS, the System ID is 796 (Hex). NAC values always start with 79, and vary from site to site on the third character (Local towers are 79D,79A, 79B, etc..)317 (decimal) = 13D (Hex). Could there have been a typo?
(Unless the scanner shows the NAC in Hex to start with, then I'm out of ideals.)