Unless you're growing from real seeds instead of tubers, your potatoes will "grow true." Potatoes grown from tubers are actually clones of the mother plant. So, they will have exactly the same set of genes as the plant they came from.

You won't be growing "seed" or saving seed. You'll be planting potatoes and growing more potatoes from those you planted.

Your primary problem will be figuring out how to save/store/prevent rotting so the potatoes you harvest this year can be planted the following year.

Fingerlings are small to begin with so they decline more rapidly than big potatoes do. And with their sugar to carbohydrate ratio they don't store for long.

Dave