It seems these countries do not have missions:
Afghanistan
Algeria
Andorra
Antigua and Barbuda
Azerbaijan
Bahrain
Bangladesh
Belarus
Belize
Bhutan
Bosnia and Herzegovina
Brunei
Burkina Faso
Burundi
Cabo Verde
Central African Republic
Chad
Comoros
Congo (Congo-Brazzaville)
Croatia
Cuba
Djibouti
Dominica
Egypt
Equatorial Guinea
Eritrea
Estonia
Eswatini (fmr. “Swaziland”)
Gabon
Gambia
Grenada
Guinea-Bissau
Holy See
Iran
Iraq
Israel
Jordan
Kazakhstan
Kiribati
Kuwait
Kyrgyzstan
Laos
Lebanon
Lesotho
Libya
Luxembourg
Malawi
Maldives
Mali
Malta
Mauritania
Mauritius
Moldova
Monaco
Montenegro
Morocco
Myanmar (formerly Burma)
Namibia
Nauru
Nepal
Niger
North Korea
Oman
Pakistan
Palau
Palestine State
Qatar
Saint Kitts and Nevis
Saint Lucia
Saint Vincent and the Grenadines
San Marino
Sao Tome and Principe
Saudi Arabia
Senegal
Serbia
Seychelles
Slovakia
Somalia
South Sudan
Sudan
Suriname
Syria
Tajikistan
Timor-Leste
Tunisia
Turkey
Turkmenistan
Tuvalu
United Arab Emirates
Uzbekistan
Yemen
At least without verifying there are not any missions that have 2 countries besides Belgium.
