Perhaps it will make a difference, I don't know really. Those that made the suppermods must know better how the game works at startup. Most models will be used throughout the war though, so there won't be much difference in 39 or 44. Also you'll have to allow for some overlap in the years since you cannot promise your crew you'll be in home-port in time for
Weihnachten.
You do know that GWX allready splits up the campaign in the major sea areas? Atlantic(default), Black Sea, and Indian Ocean. The Merged campaign has it all, so use that only if you need to cross over to those regions.