A couple things worth mentioning:
1. Just because potatoes can be planted early, doesn't mean they have to be. As Joannabanana says, planting much later is just fine, as long as you don't use a long season variety.
2. If you live in an area that experienced deeper than usual snow all winter this season as I do, my soil thawed before the snow melted, despite the extremely long, very cold air temperatures. Most years, the ground is still frozen as the snow melts. My snowdrops and corydalis solida, are coming up at normal times this year. This, even though the snow melt is much later this year. So I am planting cold tolerant crops no later than other years.
