The initial assigned grid is the "official" one.
Many of the radio messages in GWX are there for the immersion factor... but many of them also serve very real purposes... It is your decision to make...
Many of the radio messages are part of DOZENS of scripted historical events that occur at correct dates and times. (Bismarck sinking, D-Day Invasion, etc etc)
Every major naval engagement in the Atlantic, Black Sea, and Mediterranean has been scripted in GWX. Many historically accurate events occur in the Indian ocean and Arctic regions as well. (Refer to GWX manual)
You will get a feel for what is accurate and what is there for immersion.
