All saved potatoes make sprouts when in the house in a warmer environment. The only way you can prevent it is to keep them just above freezing and most of us home gardeners can't do that. Planting with long sprouts wouldn't make nice potato plants. Break the sprouts off and wait until the weather is right for planting. They may make short sprouts before planting time but that's OK. There is still plenty of good in the potato to grow the potatoes.

We have grown potatoes for years. My husband removes the sprouts at this time of year and then cuts them up with 3 or 4 eyes per piece a week before planting then leaves them outside in the garden shed for the cut part to callus over before planting

Thanks, dowlinggram. I just found a book about potatoes that suggested a few things you mentioned but with not enough details. Your explanation makes a lot of sense. I didn't realize the long sprouts weren't that useful, so I will take your advice!

I store my potatoes at 7°C and they eventually start to sprout, and as pointed out, that doesn't harm the eventual outcome. I read about a process called "chitting" to prevent the long sprouts. I tried it and it worked very well, but you do need some specific conditions. I placed all my 100 potatoes designated for seed in large trays then put them in my shop on the cool floor, in front of a sunny patio door. What you are trying to do is get them into very bright and cool location. The eyes set out really tiny sprouts that appear to be actually clusters of tiny leaves. When I planted these chitted spuds out, they nearly bolted out of the ground. They were really ready to grow.