Firstly, hello and
Regarding your questions: just because mating occurred doesn't guarantee fertility, of course, it's always a possibility to keep in mind. Something could be wrong with your rooster and/or your hens. If you wormed them with something quite strong within the last two weeks, that could account for this.
There's also plenty of breeds or family strains of breeds wherein the males cannot be relied upon to cover that many females each. I've had roosters who were hard put to fertilize the eggs of one hen, and other roosters who could manage to "cover" dozens of hens. Do your boys have favorites? It's quite possible they're not actually mating with all the hens. Also, some hens manage to mate without getting "pregnant" by any rooster they don't like. Studies have shown they can not only deposit unwanted sperm but (as is the case with females of any species it seems) they also have spermicidal factors within the reproductive tract that eliminate certain sperm, sometimes favoring one male over another, or one gender over another, and sometimes killing indiscriminately.
But it's more likely, I think, that it's just too soon. Some eggs seem to develop swifter than others. I've seen that white spot on infertile eggs too.
About them getting cold, I wouldn't worry unless they seriously chilled. I had eggs left overnight at all stages of development by incomplete-broody hens who would abandon their sneakily hidden clutches overnight to roost like normal during winter, and I also had other eggs I thought were infertile that I left uncollected while very ill, and all of them hatched. Until they're actually zipping the shell, it seems they can return to dormant state when the temperature drops too low to develop. If it seriously gets frigid though that's another matter.
Healthy eggs though can take an amazing amount of abuse and neglect. As far as I know the two most important periods for steady and correct incubation are early development and when they're actually hatching, and everything in between can fluctuate to some degree without fatal harm to the embryos.
Best wishes.
