I have had no less than 6 V3 SDDS cross my desk and none of them had a 1 piece case back. Im not saying that they dont exist, and I know that the 2 piece will fit the cases that came with a 1 piece... So theoretically, it could be a situation where the little worker who put it together pulled the case back from the wrong bin. OR they ran out of the 2 piece and just started sending them out with the 1 piece.
And I have had (2) V2's and they BOTH had a 1 piece case back. If it has a beveled date window (and hasnt been modded) then it is a V2 or a V5 or ultimate and NOT a V3.
If there is ONE THING you will learn about replica watches and particular the SDDS... there is no real consistency!
If you can post a picture of the dial it would easier to tell you what version you have. The V2 watches had REALLY domed hour markers. The looked like little mounds in a metal surround.
The V3 were much more flat and even with the surrounds.
Good luck, but post a pic and we should be able to figure it out for you.