Yes, coco is reusable!
After the old grow, make sure to flush it — when you dried it out, all the salts stayed inside. You probably don't want to overdose your young plants :)
After flushing, make sure to buffer it with a CalMag + coco A+B nutrients solution (light concentration, ~30-50% of normal strength). This will give a good start on old coco and restore the balance.
Happy growing! 🌱