Yes, the design is routinely changed to make the currencies more safe against falsification. And the old currency is often taken out of circulation simply by we

Yes, the design is routinely changed to make the currencies more safe against falsification. And the old currency is often taken out of circulation simply by wear and tear. But it is the sign of a stable economy that legal tender does not have an expiration date. "Note that it is U.S. government policy that all designs of Federal Reserve notes remain legal tender, or legally valid for payments, regardless of when they were issued. This policy includes all denominations of Federal Reserve notes, from 1914 to present as per 31 U.S.C. § 5103." https://www.uscurrency.gov/acceptance-and-use-older-design-federal-reserve-notes https://www.uscurrency.gov/acceptance-and-use-older-design-f... Despite not being legal tender anymore, the Deutsche Bundesbank changes your DM notes, if they are after issued after 1948 (https://www.bundesbank.de/en/tasks/cash-management/dm-banknotes-and-coins/-/exchanging-dm-for-euro-616928 https://www.bundesbank.de/en/tasks/cash-management/dm-bankno...). The currency has been introduced in 1948. If you feel inclined to do so, you can spend a 1 Yen note from 1885 https://en.wikipedia.org/wiki/Banknotes_of_the_Japanese_yen https://en.wikipedia.org/wiki/Banknotes_of_the_Japanese_yen So, inflation and wear and tear takes old notes out of circulation rather than expiry.