I used this guide last summer to walk the first half of the GR10 before bouncing over to the alps to do the Tour de Mont Blanc and the Haute route to Zermatt.
This guide has everything you need to survive the trip. Of course, over time things change. some epiceries, gites and campgrounds will close or change their hours, but that is some of the fun of this trip. the uncertainty of where you are going next.
Over 300 km's, i only found one major error in the guide, and i think that error was due to the cutting of a new logging road which made finding the existing logging road much more difficult.
I guess if there was a problem with the guide is that it didn't explain well how difficult some of the optional excursions were. I forget the name for the non-main trails, but I was scared off due to a lack of a detailed description about potential dangers of various alternatives.