You can't get snowy without the harlequin gene, so to get snowy from a gray, you need to either already have a snowy to cross to it, or another color that has the harlequin gene like Spot, or a duck you know to be carrying harlequin.
Same with Spot, only in that case you also need one li Light Phase gene too, and the same applies to it as to harlequin. It needs to already be there or you need to have a duck you know carries it.
Yes, I'd always read in books and online that Silver in the UK was our Snowy. That is why I said that in the original thread that spawned this one. But if the genotype of Abacot is this:
M+M+ li^h li^h e+e+ bl+bl+ C+C+ B+B+ r+r+ D+D+ Bu+Bu+
As
@Upper Brook House Farm says, then that is indeed the same as our snowy.
Speaking of which,
@Upper Brook House Farm I was going to ask in the other thread but didn't want to derail it further. What is the genotype of your Silver ducks?