Collectible value aside, let's say I have some old currency – bank notes and coins – from another country, perhaps acquired from a relative who visited many years ago.
In the case of countries or regimes that obviously no longer exist, is it safe to say the currency has no legal tender value?
What about for countries that do still exist: Is there any way I can check if old notes or coins are still considered acceptable legal tender? e.g. a reference source listing country and oldest date for valid currency? Or, is this necessarily a research exercise on a case-by-case basis?
What kinds of events might render old bank notes or coins no longer acceptable as legal tender in their country of issue?