All of my breeds are of Heritage type, too. Despite having no supplemental lights, I still get about a dozen eggs year round from those who do continue laying during the winter.yes, this is very true. They need enough time to eat and drink to keep warm.
But, I’ve never heard of backyard chickens (even with supplemental light) lay year round -except for the first winter when they are still pullets. Even then, it seems they slow down somewhat and don’t lay quite like in the spring and summer. I’ve never had production hens myself, so I’m not experienced there. My heritage breeds have supplemental light, yet they slow down in the winter-even the pullets.
I do still need to put in a couple windows in the mixed flock coop henhouse, for natural light. The other two coops have a window, so they have some form of light.