I think what you may have seen in the NOTAM is the aerodrome reference code, which gives an indication of the (in this instance) size of aircraft for which the taxiway is suitable.
Code C would allow a/c with a wingspan of between 24m and 36m, and an outer main gear span of 6m to 9m.
Not entirely sure what the code for a 757/767 would be without resorting to the Big Anorak Spotter's Guide To Trivia, but Code D is 36-52m and 9-14m respectively, Code E 52-65m and 9-14m.
Hope it is helpful.