I am going to just express an opinion, Bob.

Leaves do the work of photosynthesis for any plant. They "make" the sugar & starches that come together in whatever crop that we hope to harvest. The plant requires very little in the way of nutrients from the soil.

Maybe 90% of the food value in potato tubers comes from photosynthesis. Yes, the tubers are "modified plant stems" and, they are underground - or, should be. Still, it is the plant's leaves that are putting the great majority of the food value into those tubers.

Lower, older leaves may lose some productiveness and, certainly, the tubers need to be covered over they will turn green and become inedible. Still, I have never understood the idea of only allowing a few of the plant leaves to stay in sunlight while more & more mulch or soil is brought up around it. Growing potatoes like that is not for me. I just mulch with compost - a task that I will begin tomorrow.

Probably, pruning can be done just fine on plants that are out-of-control. I doubt if it will seriously set the plant back but, I would expect the yield to be diminished.

Steve

I should have clarified something else....

These are by no means russet potatoes. These are mini German butterball potatoes.

I have mounded up the suckers twice, the foliage is now 18-24" above dirt level.

Bob, I don't think huge above ground growth is undesirable at all. I agree with Steve that leaves are producing the energy the plant puts into the "fruit".
Last year I grew Marris Piper for the first time and they were enormous plants. They topped out at 4 feet!
And my yield was spectacular. So if it were me, I'd leave them to grow.

Ok. Will do. Thanks people!