dont know if theres any scientific evidence supporting my claim
BUT
if i try and germ seeds i know are old this is what i do.
1. pinch test em. if they smash.. they no good. time already saved.
good viable seed wont crush when pinched between fingers with moderate pressure.
2. after they pass test one...they go into fridge for a few (2-4) days. my reasoning behind it.......is this; in nature, seed falls off or comes in contact with the ground at the end of the growing season when temps are cooler. in a nutshell i try and simualte and stimulate the process thusly. cooling the seed to simulate winter. dont know if theres factual evidence behind this but it works for me. even for old pure sat seeds that really dont see a true "winter"
moving forward....
3. after the "cooling" step, i take them out and let em come to room temp, then into a cup of rainwater/tap/fiji bottled water, they go. after a day of soak they go into a papertowel and on to step 4.
4. placing seeds about 4 inches apart in the paper towel (moistened but not SOAKED) i gently fold em over covering them and slide the moistened papertowels with seed in a plastic baggie and set on a gas stove or a cablebox, or a heat pad made for germinating if youre a "moneybags." this adds a lil bit of warmth which, i find, seems to help out older seed a bit. look around. im certain you all have something electrical that constantly makes a lil warmth. cable boxes and gamers playstations come to mind.
5. older seed can be slow going so be patient. some can take 7 days or more to pop.
6. with older seeds, i generally wait til a good amt of "tail" is exposed from the seed "husk"
i seem to have better luck when theres a lil bit more of that initial tap root showing than popping it into dirt when the shell is just cracking open...
if you place the germed seed into soil its imperative that the soil mix is loose airy and fresh (not reused). its just makes for an all around better enviorn for your newly hatched lil one.
theyll grow pretty much in any soil, but, the early stages, imo, are critical for how things will progress with it in the future. a good healthy start is KEY with older seed.
also....
alot depends on how they were stored over the "long haul"
if a "cool dark place" means a box on your dresser for a long period of time exposed to temp fluctuations, they might be a bit harder to pop.
storing seeds over the long haul is best done in the fridge.
be certain the stock is TOTALLY dry (silica gel packets) and seeds will survive right next to your produce for years.
ive done it.
good luck. hope this helps someone out there........
i know we got alot of the "well versed" crowd here.
maybe theyll stop in and offer some input as well.
but these methods have worked for me.