Hello and welcome!
The naked neck gene is semi-dominant, which means there is a visual difference between a bird that's not pure and pure for the gene. It's even apparent at hatch:
Not pure on left(giant bowtie covering a lot of the front of neck is most noticeable feature), pure on right(neck and even part of breast is visible.. bowtie is just two little puffs high on neck). As adults, they look pretty similar, just replace the fuzz with feathers..
Once old enough to breed, the chick on left if bred to say, a barred rock, will give 50% naked neck chicks and 50% that you need to sell off ASAP(aka not naked necked..). Chick on right if bred to a barred rock also, will give 100% naked necked chicks, but all of them will not be pure for the naked neck gene.. in other words they will look like the chick on left.
Reason I mention all that is because there are quite a lot of naked necks, either from hatcheries or backyards that aren't pure for the gene. So chances are very good if you buy some and breed them, you will notice a percentage of chicks come up not naked necked.. which can seem confusing at first.. it's simply the parent(s) not being pure for the gene is all.
BTW some people believe only the ones completely naked necked, no bowtie at all are the only ones pure for the gene, that's not true.
I'm sure most will tell you they are indeed docile, interesting AND beautiful birds. Pretty decent producers too- of eggs and meat.