This is a really tricky one. We have 12 months expiry on ours, we also track every single one so if it is lost they can still use it. Therefore we do everything we can to be fair to the client.
I would worry about having no expiry date, because let's face it nobody actually has all of the 'unredeemed' voucher money put to one side until it is used.....so what if after the salon had been open 10 years and everyone who hasn't used their vouchers came in all at once over a few months?! Surely it would put a small salon out of business? Just a thought