Countries competing in all editions of the Olympics
Name the countries that participated at all summer and winter Olympics without missing any edition.
Including athletes competing under the Olympic Flag (e.g. Moscow 1980)
One of the countries participated in the equestrian events of the 1956 Games held in Stockholm in June, but did not attend the Games in Melbourne later that year.
The second summer answer is odd: the athlete from this nation participated as an american without being one yet! IOC stated later that the athlete was not American at that time
The USA didn't compete under the Olympic flag in Moscow 1980, they didn't compete at all. However, a lot of European countries which did not want to boycott the games, but still wanted to show disapprovement of the invasion of Afghanistan, competed under the Olympic flag (for exemple France, Great Britain or Switzerland)