I had only 50% success this yr with some new, small tubers bought in. They werent expensive, so not too unhappy really.....
The big ones that I grow in pots from one yr to the next, including chocolate cosmos, are all over wintered in their wrapped pots & covered with fleece 'hats' in an unheated part-glazed porch that can be cold, but frost free.
I did end up tipping the non-starters out of their pots, & checking things out. Yes, still solid tubers with growing points, but nope, just didnt want to get going, despite the warm sunny windowsill.
I planted a couple of dahlia bulbs I bought in Lidl about a month ago and can't see any sign of them. I planted them when the cold weather ended. I've seen other bulbs and shoots appear, especially in light of the warm, sunny weather of the last week or so.
Are these something that needs to be planted in pots and kept in greenhouses at first? I just put them into the soil.
Chances are Tomsk that they're too cold still. They may have survived, but I'd check them out, very carefully, to see if any signs of life. IME They need to be started off inside, with some heat- windowsill in my case- & not put out/planted out until after the risk of the last frost for your area. J.