I would leave the dux eggs for the Muscovy hens too, i have heart that Muscovy™ incubators are the most reliable and technologically advanced. They even include an active defense system for the eggs and the ducklings.Oh, on another note, I've been gathering duck eggs to try again. Strangely, there were six in the coop this morning. And I only have five females!
Muscovy have been busy too, but I've been leaving their eggs so they go broody.
And it happened to me too in the past: Three hens and four eggs in the morning and there were three eggs the morning before. I assume one duck laid an egg late in the afternoon/early evening and another one in the morning.