Just wanted to mention what I read about shallots bolting - cold induces it and heat suppresses it - and besides genetic resistance/proneness to bolt I also read that juveniles (from seed) are more sensitive to the cold trigger. I also read that large sets are more prone to bolt than small ones.
Our springs are so cold, I think to be successful in producing bulbs we will have to stack all the genetic advantage we can get plus also use small sets.