there is no complete list of regions.
Its all defined by the corresponding *.REGIONINCL file that is linked from a .scenario file
the region numbers in that .regionincl file tell the game wich of the region to use in the .cvp file (wich is also linked from a .scenario file)
just check the scenario file you want to edit / or have it as base and then check the corresponding .regionincl file to see wich countries are in that scenario (and wich numbers are not used)
It is not as easy as you say.
For example: I'm trying to create "Tonga" and I use the number 2214 that is not in use in my BIPUCW.REGIONINCL but instead of create Tonga I get "Christmas Island". Is there Christmas Island in any list? No, I'm afraid not but it appears in the game after cached. That's the why I ask for a REAL list.
If i start with a blank slate - i could make 25 totally new regions in my mars mod without having a complete list of predefined regions- i just had to set the owner number in the infoset section of the mapeditor - put the same numbers in the CVP and into the .regionincl file.
But i think you were caught by a text-replacement that is done in the Localize/LOCAL<your LanguageISOcode>/Scenario folder - look for file with the string "localtext-regions.csv"
the replacement text goes up to:
2214, "Christmas Island", , , ,
2215, "Kiritimati", , , ,
2216, "Western Samoa", , , ,
2217, "Samoa", , , "American",
so 2218 seems save - check the 2 other files too - just to be sure
(in my mod i seem to have nuked that file - so no issues for me)
my mods viewtopic.php?f=79&t=25932
(even techs and units for everyone - AI will own you too)viewtopic.php?f=87&t=26151