Hi,
If you are using the "coupon generator" in HikaSerial ; it will create HikaShop coupons.
These coupons are just classical HikaShop coupon and they won't have any single link with the serial which generate them (except that the coupon code will be the same than the serial data).
So, in that specific case, the question is not related to HikaSerial but to HikaShop itself (and the answer will be "no, use points instead").
If you are using a random generator, the gift certificate will be something "physical" ; a real paper that you can give in a store and which will be consume by the store (so the customer won't be able to use it twice).
In that case, you can imagine that the manager can use the "serial extra data" in order to store an information and will re-set the serial as valid. So the next time the customer will be able to give that serial to be consume and the manager will see the "extra data" for the extra information.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.