Unless the only coins you collect are extremely modern, you should be concerned with what has been evolving using Memorandum of Understanding (MOU) between the United States and an increasing number of other countries regarding the import and ownership of foreign and ancient coins.
A MOU is unlikely to impact a modern non-circulating legal tender coin sold to raise funds for a government, mint, or organization. Even some 20th century circulation strike coins are by at least one foreign government now being considered to be national patrimony that may no longer be exported or owned abroad.
A MOU is a legal document describing arrangements through which two parties agree to work together to meet an objective. The recent history of MOU regarding import or ownership of certain foreign coins into the United States has basically stacked
