The available points from the guest account are only deducted when a redemption code is honored, thus, allowing the guest to generate multiple codes even when they do not have sufficient points in the account.
For example, there is a guest who has 830 points in their account and generates code for $10 off redeemable for 500 points.
As the $10 off redeemable is not yet honored the guest is able to generate the other code for $5 off redeemable for 250 points as the 500 points will still be present in the guest account.
Now when the guest tries redeeming the first redeemable $10 off it will be successfully honored and 500 points will be deducted from the guest accounts. When the guest tries redeeming the second code he will get an error message 'Redemption not possible since the banked value is less than the discount' as there are not enough points left in the guest's account.