Planting potatoes is an act of faith, in many ways, and waiting for them to reach the right size can be almost unbearable, since they are buried so deep you really have no clue from the tops as to how things are going down there. From experience with other vegetable crops, Ive learned the hard way that the fancier the foliage, often the poorer the yield, tomatoes being one exception to all of this--possibly because the fruit needs the leaves for shelter, shade, and to bring nutrition to the tomatoes as sunlight.
Peppers prefer one over the other, and usually good leaves and tall vigorous plants mean a really good harvest of leaves but not much else.
And today I decided to pull up one of the sadder looking potato vines just to see what kind of progress was being made. and up came one very small potato and one apple sized potato. this being the end of July, i would say with luck I might get a fair yield out of what I planted.