I don't want to intrude, but I suppose there's a couple "tricks" I've had to do over the years at times and maybe they could help here too. I have had a couple cases where a seed (scuffed, soaked etc) did not sprout after 3-4 days and was ready to give up. However, by placing a bit of pressure on the seed halves; I was able to "crack" the seed (again after 3 days of soaking) and from there it would grow fine. I cannot say why those couple did that as they were soaked and scuffed....and sank; but there is no way they would've opened without my help.
One other thing I've done, though typically after they show a tip; is a sort of "steam" method. Where I put them in the moist paper towel and inside a sandwich bag. I leave a pocket of air in the bag when sealed and then set it out where it can get good sun. The greenhouse effect will heat the air inside and you will get condensation (fog) on the inside. Warming sprouts up this way can accelerate cell division and biological activity, provided you don't lower the waters' DO capacity relative to temp. Also I guess this would be a natural way to create "penetrating moisture" that can further help soften seeds or access the sprout easier. So, I just do a short period until they fog and maybe hit mid 90's (air temp) inside the bag; then put back into "normal" temps.
I guess with storage; I've always just allowed the plant to dry with the seeds in them. Then I remove and store in the fridge (not freezer). I don't sprout that many for sure, but I've never had a fail. I suppose the oldest I've tried from this system is 3 years though.
Sorry to butt in. Just a couple things that have helped me with oddities in the past. I'm sure these things are probably considered wrong and that I'm the only one who would do it :D