I utterly believe the sucess in germination has some logic link with humidity and energy the seed has stocked into it.
What happens when a seed is stocked for too long is that it looses it's humidity and it becomes harder for it to open it's shell.
Therefore it's not lost yet, you hidrate it for up to 24h in a glass with water, if possible deepening it in water. Then switch to paper towel method. The idea is to soak and make the shell "more loose", then keep humidity @ 80%.
Genetics might influence the germ rate, but I think being stocked for years affect germ rate more intensively.
Like seeds from the same crop, if they were collected too young... will share such bad trait.
All you gotta do is to develop them properly, till the plant start opening the "seeds" compartiment, like intentionally spurting seeds out. This is a fully matured seed.
I choose big seeds, dark shell, hard (although I'll never trully try to break it with my fingers, cos every seed, strong or weak can still germinate!)
Store it in a airtight, dark container... and the most important, keep humidity low, if any...
Some growers store their seeds for 6 months, simulating the winter, in order to reproduce the same natural gap in seasons, till germinating them.
Wish you luck with your experiment, bro!