More information to follow,
The .REGIONINCL files are used to choose what regions are included in scenarios. They are plain text documents with a header and a list of regions ID#s that match entries in the .CVP file. If an area of the world is not listed individually in the .REGIONINCL file or part of a group included in the .REGIONINCL file that territory will appear in game as "World Market". This is considered an error and may cause unexpected results.