[nso]

In Mexico that's the US, so maybe the poster is from Spain.

The doubling of the letters (e.g., "EE." for "Estados" and "UU." for "Unidos") follows a convention in Spanish where plural abbreviations are indicated by duplicating the letters. The correct form would be "EE. UU." This practice aligns with historical Latin abbreviations (e.g., "SS." for "Sancti" (plural) or "S." for "Sanctus" (singular)).

[samoit]

¡Correct!. I would not be able to explain it better.