Just talking through my hat,
Moisture may also make a difference to storage life. We are told that it does for potatoes and it is likely one reason that our basement, with its forced air furnace, isn't so great for potatoes. There's a door between the storage room and furnace room but it may not make much of a difference.
Certainly, when the bulbs need to be harvested during the year it would make a difference as it does with potatoes. I returned to the garden center for just plain-old Russet Burbank because I wasn't willing to order a late variety to supplement our selection of early types. I have focused some years on the early that I have nearly gone into "crisis mode" trying to keep them out of too warm temps.
When I first grew shallots, likely French grey and Dutch red, I had only a few and neglected them on a garage bench after harvest, right through the Winter, with freezing in the garage, they were okay. This has been true with the varieties from seed that I have grown. I'm reluctant to admit that it has worked so well that I have continued the practice but, keep in mind that "your mileage may vary!" Anyway, many of the shallot bulbs were sprouting when they were set out recently but that is quite a long storage life (in the most casual of circumstances). I don't know if they would be in better shape in the basement with the Candy and Walla Walla but shallots certainly fill some Springtime needs for us.
Steve