Good to know that your letter arrived in safe condition.
I have only one experience with African postal service (South Africa), in which I lost the coin. One experience with South America (Argentina, everything went well, however took over one month to receive the letter). Have received some half dozen letters from US, lost one. No letters from Canada. Plenty of letters from EU, no major issues. About 3-4 letters from Australia, lost one (however the dealer was gracious enough to send all the coins again which arrived safely). No letters from New Zealand or other Oceania countries. Only one letter from China without any issues, not a single letter from Russia.