I have tons of old seed and I rarely have issues with no germination. Usually when I do it's because of weather issues or my error. For a long time I believed lettuce seed had to be fresh to germinate. This Spring I tossed some old seed outside not expecting more than a couple of heads. Practically all of the seeds germinated! I guess the weather conditions were perfect.
The point is, I'm not sure how useful the information would be since there are so many factors involved. I'm willing to try old seed and if I only get a couple of plants that's fine with me. I do swaps to try out new seeds to see if they work for my area and conditions. Even if you only get one plant you can let it go to seed and get fresh seed that way.
Some people only want "new" seed and I doubt anything people write will change their minds.
