My country (Czechia) issues both 1 year and 3 year versions of the International Driving Permit. The 1 year version is supposedly issued under the 1949 Convention on Road Traffic, while the 3 year version is issued under the 1968 Convention on Road Traffic. Notably the United States is party to the 1949 convention, but not the 1968 convention.
But is the 1 year version really necessary for any country that accepts IDPs? Can I just go ahead and get the 3 year version instead? I'm planning to travel to South East Asian countries, which usually require IDPs at police checks.