Regarding the recent apparent controversy over a Coles discount petrol voucher, it was/is interesting to note a post that seems to have decrypted them (and remains published?)…
As with PINs and passwords, (bar)codes themselves by definition are unique and cannot be forged: they either work and are (electronically) accepted, or do not. They can, however, be illegitimate, unauthorised or unsanctioned.
Besides this, there are three types of vouchers: single-use, exclusive (multi-use), and general (non-exclusive).
Single-use: Once used, these become expired, no longer valid, and cannot be used again (by anyone).
Exclusive: These are intended for use by only one person or group, with strictly exclusive ones linked to those eligible by their account or other identifier.
General: Eligible for use by anyone.
To avoid future confusion, I proposed that we start using these terms more often :)