What's interesting to me is that the meaning of 'counterfeit' is being shifted. Counterfeit does not mean actually counterfeit, it means 'we couldn't process this stamp', which is a different thing altogether.
I guess that either the Royal Mail's system is failing to read the bar code correctly, or it's encountering a bar code it's already seen before, and assuming it must be malicious. But in the latter case, there's no basis for saying the second use of the code is the counterfeit and not the first. That is, apart from doing actual forensic analysis on the stamp, which my guess is they are not doing—not in every case at least.
If someone called me a counterfeiter, or even just said I was benefiting from counterfeiting, I'd be pretty angry. Especially if I found out they were accusing me without any evidence, without doing any diligence beforehand, and possibly as a consequence of their own error.
That would mean there's no encoding to crack, but it could still be going on if it's an inside job. Someone has access somewhere in the production process, notes valid codes. Could be a camera hidden somewhere.
I guess that either the Royal Mail's system is failing to read the bar code correctly, or it's encountering a bar code it's already seen before, and assuming it must be malicious. But in the latter case, there's no basis for saying the second use of the code is the counterfeit and not the first. That is, apart from doing actual forensic analysis on the stamp, which my guess is they are not doing—not in every case at least.
If someone called me a counterfeiter, or even just said I was benefiting from counterfeiting, I'd be pretty angry. Especially if I found out they were accusing me without any evidence, without doing any diligence beforehand, and possibly as a consequence of their own error.