Actually, it supports originals, including CI1, though you have to create a mod specifically for it as the game is too different. It also supports other games, e.g. Island Wars or Piggly. The “almost” in
means that it doesn’t support mobile versions well and doesn’t support the oldest games at all.
The reason weapon reskins from CIU work on new episodes is because the file structure is so similar that mods conveniently fit the episodes as well.
If you want a fun fact, the older (v1.2—v2.0) IAMT versions were called CIMT because I didn’t know it works on other games as well. v1.0—v1.1 was called CIUMT, so neither me nor Neonova_Solara were creative with that. The mode selection menu everyone hates also wasn’t a thing until v1.2 — you had to pass the argument in the command line manually. The menu and the whole interactive thing was OneWingLunarian’s idea.
This also means that there was never a CIMI, as the installer appeared some time after.
Another fact is that IAMT wasn’t too intentional. The original project was called “CIU string decoder encoder” and only had modes “1” and “2” to help with manual file editing. The whole modding aspect appeared around CIU v35 as an alternative to counter limitations of the quickbms script. The “decoder” name still lingers in the project folder name. v2.0 solved v35’s new WAD format, v3.0 introduced mod files and IAMI.
Given how development went until it stalled, there may still be some hidden functionality in IAMT/I that’s not documented in the changelog simply because I forgot to write that down.