Not sure if anyone else has spotted this but I could not find it on the forums. I have just downloaded the Gamersgate version and the total download size was about 334MB which I thought was small.
Looking in the temp folder that contains the files I see the steam installer are the following two disk images:
Naval War Arctic Circle - Beta_disk1.sis
Naval War Arctic Circle - Beta_disk1_0.sid
If you try to install the game then steam starts, asks for the activation key, and the proceeds to download the game from scratch (1270MB).
My broadband isn't super quick so I am still waiting for it to download and I am sure it will work, but I did think this initial "BETA" download from Gamersgate was a bit odd as it seems to be useless to the installer. Could it be they have the wrong version?
I have no idea why GG chose to make a beta available that would need to be refreshed.
When we changed from beta the folder name also changed, so beta users needed to re-download everything, not just the parts that had changed. Lessons for next time: use the real name of the game as a folder name from the start.