Wouldn't it be better to just make arrows poison their target once, after which the poison wears off?
That way you don't have to introduce some new complex mechanism of action to deal with just a bunch of poisoned arrows but instead you have two stacks - still poisoned and not poisoned.
For a sword or a spear, I understand the concept of poison acting more than once - it's a big piece of metal and you can wound and poison multiple enemies with it.
However, for an arrow/quarrel, it's a small amount, probably just enough for a single shot.