That was one of the things i tried to stay true to in the WWIV map. Yes, there is need to combine some areas while splitting others up, some leeway is also required in some areas.
Some examples
In North America the area called Nebraska is quite a bit off. While it does cover Nebraska, it also covers much more but I mapped it so it kept the same basic shape of the state of Nebraska. Kansas City is shown in Kansas while we (most of us?) know their are 2 KC's and the bigger one is on the Missouri side but heck, it's one metro area and I centered it slightly off for strategic reasons. Alabama and Mississippi were combined and simply called Alabama (sorry to any Mississippians out there). In China, I was not (and still am not) as knowledgeable as I would like to be. I painstakingly poured through many maps and fairly accurately followed province lines...again, many were merged together of course but the lines are fairly accurate and the map makes for a "decent" teaching tool in that regard. Heck, even the supply centers are placed where they are in real life, it would be easier to simply place them in the middle of their territory but accuracy was key whenever possible.
Mapping the seas was just as difficult as it's not as easy finding maps with sea spaces clearly marked on them but the nice part there is the actual sea "borders" were easy to play around with to suit my needs!
The problem I did have and mention all the time was in giving some areas too much influence/power. St Helena in the Atlantic is little more than a big rock, hardly important. Similarly the Falklands, Diego Garcia, Azores, etc. Some pretty big cities are not mentioned due to being too close to another big city some smaller cities are better situated for strategic reasons, Hell, "Catholica" (Or as was originally named "The New Holy Roman Empire") is made up out of the blue as are most of China's territories (but even with all these, I attempted to focus on historical accuracies as best as possible)
Go to town on such minor errors, you will find many!
But as a general "guide" it's not that bad.