Popcorn Kernels not popping. Any suggestions to make them pop?

This is the previous day's results (1/2 tbsp water + 1 1/2 cups kernel, rest 2 days in air tight container)

Success!!!

I've been trying out different methods as I have a lot of kernels and I'm getting more into science experiments. I wasn't super exact on my controls or measurements but here's what I got:

Soaking for 10 minutes then draining: Did nothing. I found the kernels may have held onto too much moisture and still felt moist to the touch when I put them in a pot with some oil. I even let them sit for a day and popped it the next day and nothing happened.

Steaming for 10 minutes: some had popped (maybe about a 1/4 of the kernels?)

1/2 tbsp water + 1 1/2 cups kernels in air tight jar, 2 day rest: very little popped (violently) but mostly none
^^ + 1 tsp water, transferred to more shallow air tight container, 1 day rest: the 3 kernel testers popped after a while, on low heat none of the kernels popped even though the oil was hot enough. Once I turned up the heat to medium, all of a sudden every single kernel popped (sans 1 that didn't pop at all-pic is attached). popcorn tasted fine
method found here: https://www.usaemergencysupply.com/information-center/all-about/all-about-whole-grains/all-about-popcorn

*NOTE: The previous "failed" methods may have not worked because I didn't have the heat high enough (can't remember if I put it on low/low medium/medium but I think I did play around with it). Like I said, I wasn't exact with my measurements and controls (I wasn't planning on this to be an ongoing experiment) but these are the results I got. I got pretty excited when I saw all these kernels finally popping :)

I'm guessing it is old and dried out. Which sounds counterintuitive, since popcorn appears pretty dry. However, what causes it to pop is the rapid expansion of moisture inside the kernel. That said, nothing lasts forever, so when you discard what you have (the bad news) and buy a new batch, transfer it to a glass jar with a tight lid and place a piece bread inside the jar. Replace the bread each time you make a batch of popcorn, which should probably be relatively often (the good news).

I read something once about soaking them in cold water and then draining and drying them before popping.
Did not try this as popcorn is so cheap we prefer to just buy new.