Learning about Potatoes!

Hello! Household 7 here. ( pardon the joke)
Recently we planted potatoes, 14 seed taters in one of our garden boxes behind the shed.
We actually planted two sets of potatoes in two boxes. But this post is looking at the first box of 14 plants. I've been watering every evening and have watched the start to grow. A few of them have gotten quite big! Some of them I have yet to see at all. Which has been bothering me. I was excited to see 8 of the 14 plants the other evening. very good so far. Looking at the instructions on the bag they came in it says to add another 6 to 8 inched of soil when the plants are about 8 inches tall.  I misread the instructions and covered all of them. two days later we are seeing the three tallest plants popping up out of the soil. Looks good. Except something seemed odd, so I reread the instructions.
Just today I uncovered the smaller plants and while I was at it I scratched around for the other potato starts. They're still there and still starting.

 I'm not very sure whats keeping them from growing as fast as the others. I recovered them with soil and will wait for them to get going.

I think what I have learned so far is to follow the instructions. I will be more careful. I think if I had done it right from the start they would all doing fine, those first few are really looking good.
It's nice to know that the other starts may yet grow.

I expect i will be digging around for the starts in the second box soon, they were planted only a day after and I have yet to see anything from them.
I think I am paying more attention to them because this is our second time trying potatoes. the first time I'm not sure what we did wrong.

Thanks for reading.