1) There is a general batch of stamps and also a second batch, that is used to exchange "old" for "new" stamps. The second batch either contains duplicate numbers, or is not activated in the post system at all -> so those get marked as counterfeit
2) The barcode system has no error correction -> the scanners just read the codes "as is", without any sort of error correction / verification if they were read correctly. The incorrect numbers (wrong reading) are then marked as counterfeit
3) Incorrect readings vs some generic "list of stamps that were used" -> fake (?) duplicates marked by the system.
1) There is a general batch of stamps and also a second batch, that is used to exchange "old" for "new" stamps. The second batch either contains duplicate numbers, or is not activated in the post system at all -> so those get marked as counterfeit
2) The barcode system has no error correction -> the scanners just read the codes "as is", without any sort of error correction / verification if they were read correctly. The incorrect numbers (wrong reading) are then marked as counterfeit
3) Incorrect readings vs some generic "list of stamps that were used" -> fake (?) duplicates marked by the system.