From: Federal Way, WA
I think everyone does it differently, but here's my procedure. I use one slot for the game as it is in progress, and this is also the file I pass back and forth to and from my opponent. Let's say it's Slot 50 (since it is, in my current game). You're correct, this is wpae050.pws. The internal name is simply whatever he named it, since he's the Japanese player.
When I get a new turn I immediately open it and save it in a second slot, in this case 6x where x represents the units digit of the turn number. Thus, Slot 60 is used for turns 10, 20, 30, etc.; Slot 61 is turns 1, 11, 21, etc. This gives me an archive of 10 "start of turn" files, with internal names to that effect (Dave vs. David - Start of Turn 12).
Before ending the orders phase I do an end-of-turn save to the 7x slot, so I also have a 10-game archive of end-of-turn files. After this save I end the orders phase, save to Slot 50, and hope I remember to send it to my opponent right away!
By always using the same slot (50) for the active game, even in the middle of the turn, I never have to worry about overwriting an archived version. By keeping the archives I can go back and review anything for 10 turns, and I have them available in case we need technical support. Of course, all the emails are also archived, so I have every turn available there if I really need one of them.