The date when the initial series of euro banknotes ceases to become legal tender might be introduced well beforehand. On the other hand, the banknotes of the very first sequence will always keep their value: they may be exchanged for an infinite stretch of time on the Eurosystem NCBs. See https://judahzsahq.blazingblog.com/29632387/5-easy-facts-about-buy-euro-e20-bills-online-described