Hi,
Electrode expiry, which is shelf life comes with manufacturing recommendations, but still some debate asking that ''whether its a food item to have expiry'' its not but it has shelf life which may differ 3 or 4 years as per manufacturer recommendations, and can be continued if stored in proper condition if your manufacturer accepts.
So at any case check the manufacturer recommendation and if exceed take a concurrnece from manufacturer and satisfy your client with continous proper storage records, because in any case of serious or pattern defects, before the question arises, have a proof, this shall be ongoing observation as a part of quality focus assesments.
Below is one of the australian manufacturer for electrodes, where i had to concur as proactive.
Regards,
Muneeb.