Quote Originally Posted by DOUGAL25
According to Harrington's "rule of thumb", every 1% drop in moisture content will double storage life.
Sure about that? How about the exceptions noted?
"this rule applies to a range between 5 and 14 percent" (Harrington 1972, Roberts 1979)

Quote Originally Posted by DOUGAL25
But what's the critical point of moisture content; rather, what is too dry for a cannabis seed?
In a nutshell, that's my point exactly. Drying them too much, or using a dry storage packet to artificially remove moisture (like those packets in prescriptions) isn't optimal, according to biology. We dry the seeds to harden the outer shell (which holds-in the moisture) and prevent mold in our seed storage jars. Not to dehydrate the embryo.

Quote Originally Posted by DOUGAL25
The main question is, what's the moisture content of a seed with a hole in it?
Zero. If exposed to air, and the moisture escapes, the embryo will die. A dry seed shell is not the same as a dry embryo. The membrane(s) covering the embryo retain moisture and carbohydrates (food for the emerging cotlydons) Optimal temperatures, warmth and ambient humidity (water) trigger the germination process.