A photo would help better understand exactly what is going on - it could be a worn mold or the bottle could be under blown, Both of these scenarios seem more likely than letters left out of the mold.
The more one studies individual bottles, the more it becomes clear that most bottles were produced in multiple molds. When you are looking at 19th century bottles, these molds were made by pattern makers and they frequently have subtle differences.
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The more one studies individual bottles, the more it becomes clear that most bottles were produced in multiple molds. When you are looking at 19th century bottles, these molds were made by pattern makers and they frequently have subtle differences.