Build 4580 Win Tiles, updated after ten days or so, when I pick up bolts they are added to the inventory/quiver, but also a “crossbow bolt (0)” is left on the ground, which can be used to reload the crossbow, effectively duplicating ammo.
EDIT: Nope, looks like ammo doen’t get duplicated, the empty bolt is listed in the recharge menu, but selecting it removes it from the ground and a bolt from the inventory is used. There’s no other way to pick it up from the ground.