"Unkown" casualties

https://preview.redd.it/8lwsu0883hqe1.png?width=1082&format=png&auto=webp&s=a5759d0329d2145d30cbab0e065392b44f4a59a5

R5 : While checking for the casualties, i saw that italy had 3400 dead by "unknown". I have never seen that before and i don't know what it means. Anyone ?