That advise is good for most climates, BUT a tuber will not grow in bone dry soil. The soil or mix should be continuously COOL to the touch, and if that means you have to water lightly before the sprout emerges, then by all means do it. Most area's soil have enough moisture to kickstart a dahlia out of dormancy and into producing roots/sprouts. The 'never water before it emerges' advise is to keep overzealous growers from drowning the tuber with constant soggy soil, which will lead to rot. But so will planting outside too early, with the soil temperature under 60 degrees and constant cold spring rain. Most serious dahlia growers prestart their tubers inside under lights to better control the temp and water supply, to avoid rotting because of that 'constant cold spring rain.' The unfortunate tuber in this thread probably never had a chance, and most likely had nothing to do with amount of water it received. Looks to me like it was 'dead on arrival,' with the starches and eyes dried up before the person ever purchased it.

Did they actually sprout then disappear? Did you actually see slugs? How much more dirt and mulch did you pile on top? If there's no sprouting, you probably have nothing to lose by digging up the tubers. They may well be mushy and rotten from a wet spring and the ground staying wet under an extra layer of soil and mulching. If so, they cannot be saved. If you love dahlias (and who doesn't), get your gardening experience with them next season by buying a box of tubers from Costco, Sam's Club, hardware stores, or any of the other big box stores for not too much of an $ investment. I've had good luck with those the years I buy them. They might not be the exotic mail order types, but they grow and bloom. I'm not interested in digging and storing so get fresh ones and discard at season's end.

You can do any of the following: leave them and the shoots will probably shrivel up eventually, nip them off and toss, nip them off and pot them up. (Just remember that it is a loooong time to have a cutting under lights before it can be planted out!) Often sprouting is simply that the air has humidity/warmth that triggered the growth response in the dormant tubers. However, sometimes sprouting is an indication that the tuber is rotting. If the ends and sides don't 'squish' with strong finger pressure, you are good. Early sprouting normally does no damage to the tuber, and it will sprout again once planted in late spring.

This has been a nice mild winter for tubers left in the ground. The beauty of dahlia tubers is that if you knock or cut off a sprout, the tuber will grow 2-4 more in its place. Now is a great time to dig up and divide your babies. Don't worry about damaging the sprouts, as there is plenty of time for them to grow back if needed. They will help you know where to divide your overwintered clump... Make sure you use hand prunes (not the shovel/spade) to cut the clump up (spray with hose to clean off dirt, not at the highest setting so you don't damage the protective skin). Just make sure that each piece has a sprout, and replant immediately. If a hard frost comes along to kill the green, don't worry. It's late enough in the season that the tubers will be fine and will resprout.