That article is very interesting, but a bit vague. It’s also 13 years old, and much has changed. I believe, based on context that they are giving SSC the designation of W. With one copy being what we call silver and 2 copies being white.
Have you checked out southwest gamebirds genetics pages? They’re a work in progress, but I find they are very informative. However, just like lethal gold was determined to be a separate mutation from fawn, that occurs at the same locus I believe, a lot of what we have now are combinations of mutations. I’ve been finding that with double silvers, the bad effects must occur separately to the silver color mutation because with careful breeding I get healthy chicks, and accidental, boy in the henhouse incidents still produce more sickly chicks.
we also need to remember these are lab mutations, but people were keeping and breeding quail long before you could use the internet to read about this stuff. In the Coturnix corner interview with Perry Schofield, he talks about how back like in the 60s I believe, it was common to find many mutations that we don’t see today, and people, even scientists say don’t exist, like albinos, and heterochromia. People bred what they liked, and the mutations that were more popular, spread, and others fizzled out.