I'm not very familiar with CP SYSTEM I outside of Japan, but before Street Fighter II'CE, I could only use up to 1M EP-ROM in Japan's CP SYSTEM.
However, since Street Fighter II'CE, it has become CPS DASH, and 4M EP-ROM can be used.
The 1941, which was released before Street Fighter II'CE, is a 1M EP-ROM.
I don't understand why 1941 WORLD uses 4M ROM in MAME.
The 1941 WORLD supported by MAME may be the same as the resale version in Japan.
Many of the 1941 copies that are on the market are resold.
That's all I know.