A banknote series is a collection of a nation’s banknotes in all available denominations which have been released within a limited time span. The release of a new banknote series usually corresponds with the implementation of updated security features. When a new series is released, banknotes corresponding to the previous series are gradually taken out of circulation.
A total of nine Swiss franc banknote series have been released by the Swiss National Bank between 1907 and 2016.
The Swiss National Bank is only obligated to exchange Swiss banknotes for banknotes of a new series within 20 years of releasing the new series. After that period, banknotes of a redundant Swiss banknote series lose their validity. In many other countries, including Germany, banknotes never lose their validity and can be redeemed for new banknotes at any time.
Banknote rates vs. forex rates