I just took a look at Arizona. This map
shows various trail paths. I took that map image and overlaid it on Google Earth along with the GPS track files from both Jerry and wbb. In some places the tracks from Jerry and wbb are exactly on the map path, and other places they divert from the map path, sometimes by a large distance. And Crawaddy's tracks in Jerry's file match a few short portions of the GWT. Even my own tracks north of Flagstaff accidently went on GWT for about 5 miles. I remember seeing some sort of official trail sign at one particular point along the way (35°43'4.35"N 111°49'19.89"W), but I didn't stop and study it.
If you like the maps from greatwesterntrail.org, it's pretty easy to use the Google Earth image overlay tool and the semi-transparent feature to show them in Google Earth. Once you have them in there, lined up correctly, it's also pretty easy to draw a GE path following the lines on the maps, then convert the GE paths into a GPS file. The whole thing could be done in one day.