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| Start / | Knowledge / | Safety Measures / |
| Accidentals | Differences | Errors | Kinds | Mistakes | Parallel Issues | Printers Waste | Quality |
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Knowledge / Safety Measures / Matrix Codes / Parallel Issues |
Matrix code parallel issue: the same postage stamps issued at the same time with different matrix codes |
Matrix code alignment parallel issue: the same postage stamps issued at the same time with the same matrix code in different alignments |
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Postage stamp with upright or inverted matrix code |
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