Is it just me, or do Extra2 values 1201 and up act the same as the normal Extra2 values 1001-1200? On my game, they act properly to disable other sprites with the same Extra2, and are properly disabled after saving and reloading.
Perhaps more importantly, if it isn't just me, why did it take a full year to notice this?
Assuming that this isn't a feature of my personal copy of the game, it looks like the maximum number of Extra2s you can use before the game starts choking is about 2500, and these can be any numbers you want - the way the game stores them seems to be able to prevent conflicts until you hit ~2500 separate values. Note that I've only tested up to around 1000 Extra2 values in a level, and the game crashed while loading the level with around 2800 unique Extra2s.
Edwards