Just a little something I noticed in my 1.15.2 survival world at my 'Snowy Tundra' base.
I started my villager breeder with the two from an igloo basement. Both of these were in the brown plains version clothing. About the 6th or 7th villager bred appeared in the blue and white snowy version clothing. As of yesterday, as I removed a villager to my trading hall (about 28th or 29th and of the plains type) all remaining villagers in the breeder are of snowy type. I agree that they are the ones that should spawn in this biome, but found it odd that they took over gradually rather than all at once. I would have presumed that all villagers bred here would match the biome.
This is annoying if you want to build your own swamp/jungle villages as well, besides the fact that (villager-friendly) construction in those biomes is terrible. (I guess it's no wonder such village do not generate naturally).