I don't think it's common. It's common for bad quality (hatchery) sultans I guess. My Ideal hatchery sultans are missing toenails(over 50% of them). My adult rooster and young rooster, of unknown origins are both missing nails. I think only one of my hens has missing nails and it's from the same source as the young rooster.
I either have a foot fetish or sultans have foot/nail issues and I just happen to be ocd on it. Flossy's brother had only 4 toes and was a cross beak, so I would have never used him in a breeding program. But at least he had his toenails, which gives me hope that Flossy may one day have a rooster chick with all his toes and toenails and I can replace my two existing roosters. I'm hoping this is a recessive gene.
I'm still keeping my eyes open for better breeding stock but at the same time I'm doing a project which in 4-5+ generations I hope will fix a lot of problems I see in sultans. I'm not using polish for my crosses since most sultans are already crossed into polish, I'm starting from scratch and with good laying normal chickens and silkie mixes. But this will be a balancing act of keeping my husband happy and trying to keep my numbers down. Not a problem right now, since I only have 8 or 9 adults, but I do have 12 hatchery chicks and my own sultan chicks hatching as they may. Most of the hatchery sultan chicks will most likely end up at auction or sold on craigslist since I'm being pretty brutal about what I keep.
I don't mean to come across as if I do not care about sultans. It's really the opposite, I care a great deal about sultans as a whole and want to get them, as a breed to inspire people to add them to their flocks, to preserve them. But one reason no one has a high interest except people who showis that Sultans are actually fairly useless as meat or egg birds. No one wants to feed a hen who will maybe give you 1 or 2 eggs a week when there are much better hens out there for laying purposes.
I'm tempted to order more chicks, when my husband isn't looking haha..but there's no guarantee they would be any better than the ones I already have. I noticed that Privett hatchery picture (you have to image search their crested breeds for one) is the exact same sultan as strombergs picture. With things like this happening it makes me wonder if one or the other has such bad sultans they have been forced to "steal" a image from another to act as their representative sultan picture. Or maybe privet and strombergs are actually related companies.
I have found a place which claims to have show quality sultan chicks for sale. I have to order at least 15 chicks total of any number of breeds.. But again there is the worry of they have no pictures to show more than one sultan rooster which may or may not be their own.
After the 4 toed crossbeak I'm also wary of ordering eggs. Ok, I got Flossy, my best hen, from those eggs but I also got CB and a very weak runty chick. Out of 6 eggs I did hatch 4 chicks, 2 were sickly with one dying eventually, 1 was 4 toed cross beak, one was small and I think eventually hawk food since he disappeared without a trace one day, and Flossy my girl. 6 eggs, one good chicken. Which I suppose in the scheme of things is not bad, but I can't have just one founding bloodline or my sultans will keep getting weaker and weaker. They need new blood and lots of it.
I'm not a show person. I might talk shows and standards, but I do not show. I do believe the sultan should meet certain standards, but since there's no SOP on them, this standard is in my head. I do know it would be a heavy penalty to have a otherwise great sultan who might win a show, but have a missing toenail or three. It would probably be disqualified. I just love this breed so much it almost hurts to see all the hatchery "mutts". And I mean no offense to hatchery sultans, some are very beautiful and regardless of any flaws they are still wonderful pet chickens.
4h and shows are what will ultimately save the breed as well as back yard owners who love this bird. It's incapable of saving itself with it's poor egg laying and meat providing. I apologize about my little book above but I am very passionate about sultans. I truly do love them and think everyone in the world should have a pet sultan or 10