If kept cool (preferably with
stable temperature), dry, and dark, it ought to last for a couple of years. Probably longer, with the same slow reduction in viability that one would expect from seeds.
Be careful when removing it from storage for use that "sweating" (as it'll presumably be cooler than ambient at that point) does not cause it to become damp. And be sure not to contaminate it, of course.
Have you cut it with flour (et cetera)? One tiny little pinch could, in theory, produce hundreds, maybe thousands of seeds - if it doesn't all end up on just a few female flowers, lol.
Your post... Once again, I find myself lamenting the general illegality of cannabis. If it was treated the same way that other garden (etc.) plants were, I'd be asking if you might trade some of that DDA pollen for... IDK... pepper seeds or the like. Alas, it is not to be, this year. Therefore, please make sure to store some for as long as possible
.
Maybe next year - or the next, or...