Maybe leaving the tubers in the ground all winter is best?
This will be my 5th year growing dahlias, and I discovered what I thought was a much better solution to winter tuber storage, which was to dig up the dahlia tubers after the plants experience their first hard frost in early fall(usually early November here). Then of course I clean them off, then I cut and separate them. I then separate them by variety, put the tubers from each variety into a plastic grocery bag and add some very lightly dampened soil to cover them. I label each bag, and put them into a lawn & leaf trash bag and bury them under ground in the woods so that the top of the bag is at least 6-8" under the dirt and the bottom of the bag is more like 18" below. Then I added about 6" of leaf litter on top of the dirt and branches to hold the leaves.
^^That works well to keep them cold but above freezing(done it 2 years in a row now). However, what usually happens is that the eyes start sprouting about late April even during a cooler spring like this year, and that means they cant be left there til mid to late may when its time to plant them because the stems will grow in the bags and be ruined!
So I plant them earlier than I really want to, and then they experience all the excessive rain we get in April and the first 1/2 of May. That means I had to dig them up and replant them into mounds this year(had to replant last year too). Now they have been in the ground for about 7 weeks, and I topped them at the 3rd leaf level, but they are just now about 12" to 15" tall(after 7 weeks).
However, apparently I forgot to dig up the tubers from one dahlia plant last fall, and about 2 weeks after I originally planted the rest of my tubers, this dahlia that I forgot about suddenly popped up and began growing. Well, I topped it at the 3rd leaf level too, and right now its thicker and healthier looking than the rest, and its nearly 3 feet tall now, even though it came up 2 week after the replanted tubers! I must say though, that most of the replanted dahlias are now getting thick stems and growing much healthier than before, and I think they'll be fine, because this is what happened last year too...
But the moral of the story is, maybe its best to dig up the tubers and split them after the first frost in early fall, but then replant them where you want them to grow next year, maybe 7" deep. and add some mulch for extra insulation. Then in the spring they will come up and grow healthier because they dont have to deal with being stored somewhere then planted in spring.
The difference in overall growth and health seems to be better among the tubers that were left in the ground where they were to grow. Keep in mind, we also had a cooler than average winter here, and I didnt do anything to provide extra insulation to the tubers I'd forgot about. and yet that plant's tubers never froze obviously.