I raise Swedish Flower Hens. This is the first I have heard of "Black Swedish Chickens, but I am going to research this! I also have some Rhode Island reds. All are laying just fine through the winter like yours are. I am getting around nine eggs a day from ten Hens. With no added light! My Swedes are from last spring. I can hardly wait to get the incubator up and running for spring. I also have two gorgeous Roosters so I don't need to buy eggs anymore. Mine were originally from Greenfire Farms from another breeder.
You said you "Ordered" eggs from Florida. I drove over 100 miles one way to get my Fertile eggs. The P.O. uses them like a football when it says fragile. I know, I used to work for the P.O. Even if they are not cracked or broken, they could be "Scrambled" inside the shell from rough treatment, which is why I prefer to go get my own. These eggs are very expensive and I don't want the risk of them being less than perfect. Good luck with yours, and welcome to the Forum