use notepad++ find in files feature. Select/highlight the term you want to find all the values used, Search ->> Find in Files [Ctrl+Shift+F] and point to the reference files GameInfo or whatever.

it will find every time it is used and you can see the value added. Scroll the list and find the variables or highest and lowest integers . Sometimes the highest or lowest integers used is not the highest or lowest you can use, so you will have to test anything beyond what the game uses.