I'm going to take a gander at this..... I'm sure someone will correct me if I'm wrong, which happens a lot.
Restricted pattern is a variation of Wild pattern. It is sometimes dominant, and sometimes not, depending on some as-yet-unknown factors (probably having to do with dark/light/harlequin phase). If your restricted pattern hen is homozygous (2 restricted-patten genes) or even heterozygous (one restricted gene) it would make perfect sense that some of her offspring would show this too.
Also, your hen isn't silver appleyard. She'd be a lot lighter in color overall because she'd have light-phase genes. Yours looks like a dark phase mallard (regular mallard), but with one or two restricted mallard genes (though she could be a carrier of a recessive light-phase gene).
Restricted pattern is not a 1 in 5000 mutation, it is a known gene. Most likely somewhere in the histroy of your birds someone out-crossed to either silver appleyards or mini appleyards.
That said, your birds are beautiful, and the duckling adorable.
I'm fairly new to duck genetics too, and I'm reading everything I can get my hands on. It's like trying to figure out a real-life puzzle. And it seems like everytime you turn around there's another piece of information that complicates things even more. Who needs sudocu when you have duck genetics!!!???