But he never mentions how it's supposedly harder to identify a sable merle and the risk of accidental merle/merle breedings. I've been present at two whelpings. It's pretty obvious when they're born, and there are still signs to indicate when they're older if it isn't obvious in the coat. A sable merle that is so cryptic you can't tell at birth or as it ages would be pretty darn rare. From what I understand, it mainly happens in docked breeds because the tail is usually where it's obvious. But in most of those cases the onus is on the breeder who presumably knew before they were docked.
Anyway, in collies blue or cracked eyes is a pretty good sign that an adult sable is merle. The base sabling itself also tends to come out a really light honey color compared to normal sable littermates who are quite a bit darker at birth. If I had a breeding with the possibility of sable merles, and there was a very light sable puppy but no other indication of merle I'd still note it as merle, just in case.
ETA: and I'm just going by what he says in the article. The whole thing lambasts merle to merle (which is cool), but then goes on to make some misleading statements about sable merles, and then states at the end that crossing color lines is a heinous act because it will lead to dead fetal puppies and deformed live births. Which is patently untrue. But John Q. Public who knows very little about dog color genetics doesn't know that, so now they'll see breeders with healthy sable merles and lump them with Evil Greedy Show Breeders.