Pilot charts of course are an average. They are intended for planning a route in order to minimize the chance of bad weather or to help you get a better feel for what you may find along your intended route. They can tell you it is a really bad idea to go to the north polar ice cap in January although in reality there may be a weather window that would allow you to do this..hah!
. They are supposed to be a 7 year average meaning of course that they are not going to be completely accurate. All they can do is tell you statistically what are the better routes for you to take. The only thing that is certain will be the near real time NOAA satellite
images/pressure/wind/temperature/precipitation/swell charts and less so the NOAA predictions. That's the best you are going to get.
I would still at least have a look at a pilot chart for the month you are planning on going so you can see if it is even worth going that month because of the chance of running into some really bad weather.
Good weather planning is more about probabilities than knowing exactly what is going to happen. You only know what is going to happen after it happens.