According to my experience, I think it should become common stone or junk(iron based) instead like it always does. But yes you are right that it should go at least rank 10 because maximum drop is -7 from rank 17, but it still become a rank 9 Iron Fine Sword, means -7 drop from superior alchemy is not applied
Opss, this is my signature :P
AND, the guide below was not mine, i just collect what guide were useful for easy search, sorry for sharing the link without telling..
Really thank for the guide maker :)
Pets guide
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Pets rb guide
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Quest Guide
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Information
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