Great link, Chris! Thanks very much.
Probably the reason we can store seeds in effective equilibrium with houwsehold humidity is that most people's houses are relatively dry, and they aren't trying to store delicate seeds for 25-50 years. Storing most crop seeds for 3-5 years, if they aren't moldy, is probably going to result in fairly good germination over a fairly wide range of humidities and temperatures.
But if you are trying to double or quadruple the maximum reliable lifetime of rare seeds, or seeds that might be delicate, you do have to worry about the details.
Note the conditions of the study: "water vapour-saturated atmospheres". In other words, 100% humidity outside the jar.
Also, the study did not try to determine
how many years of viability would be lost between optimum dryness and varying 10-80% RH. Only how fast those jars leaked humidity.
I always worried about humidity since I have drizzle many times per week, 8 months per year. I don't keep the house any warmer than I need to, so I worry about humidity.
I also store seeds in 2x3" Ziploks, but then I store those inside big plastic jars (that used to hold 2 pounds of peanuts or peanut butter). I agree with the author of that paper: almost any screw-on lid lets in some humidty over the years. And I paw through my stash, or add and remove Ziplooks, rather often.
I keep 1-2 tablespoonfuls of silica gel in each jar. I staple the gel inside paper coin envelopes. I bought humidity-indicating cards from Drierite (ULINE also sells them, but you have to buy a huge number as the minimum order).
When it indicates the humidty (RH) inside the jar is much above 20%, I replace the silica gel. When I run through my first 1 1/2 pounds, I'll regenrate it.
Now, instead of worrying about excess humidity, and varying humidity, I worry about excessive dryness. Gotta worry about something! I have so mnay more seed varieties than I'll be able to plant in my small yard, I hope I can save them for 10-20 years.
P.S. If you store seeds in the fridge, store them the tightest jar you can find. Let them warm up all the way to room temp
before you open the jar, or room air WILL condense inside the jar, and then, when you chill it again, even more will condense, or raise the RH inside the jar significantly. And the vegetable drawer (crisper) is MORE humid than the rest of the fridge, not drier.
There were some great footnote-references in that study, i'm hoping to find some online for free when I have time to hunt.
Ellis, R.H., Hong, T.D., Martin, M.C., Pérez-García, F. and Gómez-Campo, C. (1993). The long-term storage of seeds of seventeen crucifers at very low moisture contents. Plant Varieties and Seeds 6, 75-81.
Buitink, J., Leprince, O., Hemminga, M. A. and Hoekstra, F.A. (2000). Molecular mobility in the cytoplasm: an approach to describe and predict lifespan of dry germplasm. Proceedings of the National Academy of Sciences. USA 97, 2385-2390.
Harrington, J.F. (1972). Seed storage and longevity. pp. 145-245 in Kozlowsli, T.T. (Ed.). Seed biology. Volume 3. New York and London, Academic Press.
Vertucci, C.W. and Roos, E.E. (1990). Theoretical basis of protocols for seed storage. Plant Physiology 94, 1019-23.
Walters, C. and Engels, J. (1998). Effect of storing seeds under extremely dry conditions. Seed Science Research 8, 3-8.
Note to self...check bottle BEFORE pilling the dogs 
