If you kept it cool and in the dark in jars it should still be high in THC. I don't know how badly it has to be stored to degrade it but mine is stored as you say and it's still good since 2020.
Have you tested your 4-year-old flower? Based on what I've read I would guess some of the THC converted to CBN.
Just make RSO half a teaspoon knock out a horse.
I'm pretty sure that CBN will help with sleep. I don't know but I think whatever it is in the THC pretty much gets carried over to the CBN. I make the sleep oil out of old or new. It doesn't seem to make any difference.
I've got no idea. Today I'll try some of the freezer stuff and see if it's still good. I've heard it takes time, heat, light, and air. If it's sealed up...IDK. Maybe we should check Google Scholar. There may have been some high level research done by some big university. Not likely, but maybe. Going there now.
Yes, I tried 2 different strains, Super Lemon Haze and Chocolope from the 2020 harvest. I was wrong about how it was stored. It was in the freezer.
THC doesn't evaporate (terpenes volatize, maybe that's what you're thinking of?) but it will slowly convert to CBN over time as it ages/oxidizes.
Yeah you want all amber but it helps if your starting material is higher in cbn naturally see some lines actually produce more than others the old big bud line and its progeny put out higher than average cbn levels i been looking for it pure for the same reason as you cos insomnia but everyone these days that sells it now sells it crossed to skunk not pure so not what i want with the original seedline to make it nevil crossed a nl1 male to the pnw cutting 3 times to make the original seedline that's the one the seedbank and sensi sold before skunk was added its that line id recomend looking into if you can find it anyway hope it helps bud i think it will if you can find it