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Firstly, my “huh” was in response to the 10,000gp as I am absolutely sure it is only 1000 gp.

My bad!

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The phantom 1000gp shall appear in your inventory when you have solved both quests related to Dr. Elrath but never before you speak to Hugh because reporting it to him concludes the quests.

That's right, Hugh does give you the counterfeit gold. LUCRETIA says she hasn't spoken to Hugh yet, but has the 1,000gp. So what is the explination for this other pile of gold?