**Admin please delete if this is not the right place to post. And I'm not sure about the expired date sorry!
Found on a Facebook group that Countdown is crediting your Onecard account with $15 voucher if you have any unclaimed E-stamps due to the lack of cutlery sets.
I have contacted the live chat personally and got my $15 voucher (I think we have over 30 stamps). According to the Facebook page looks you may contact them by email or phone as well, but it's a hit and miss depending which CS you get, some got replies and said it's in the T&Cs that the e-stamps can not be converted to a voucher.
Sorry not sure about the cut off date for this, best to contact Countdown asap, and not sure whether there is a minimum number of stamps in order to be eligible for this.
Good luck!
Can you provide a link to the post or the name of the group?