For mods using the same sprite index numbers in BIGOBS, FLOOROBS, anything that used indexed sprites, etc., there are a certain number of indexes that are reserved for the original game's resources - for example, 0-127 for HANDOBS. These are persistent between mods, so if you change any of those 'vanilla' HANDOBS, all mods that reference those for an item will use the modified graphics. Indexes greater than the reserved values are unique between mods - each mod gets 1000 of each index for its own use, so HANDOB 128 will be index 128 for the first mod loaded, 1128 for the second mod loaded, 2128 in the third, and so on. You don't need to worry about these numbers, as the only time you'll see this +1000 for each mod is if you look at the output of openxcom.log with verbose logging turned on. In practice, that means each mod has its own separate HANDOB 128 and does not know about any of the other mods' HANDOB 128. Thus you can 'reuse' those indexes for each separate mod without worrying about which image resource will be loaded for each mod, as long as you don't go over that 1000 or so limit.
