However, both of them don't entail the counterfactuality , which can be cancelled by introducing an additional clause preceding them, like "我不知道你刚才有没有来这/ 叫住他，但是……(I don't know whether you were here / stopped him just now, but…)".
the counterfactuality of a CF conditional with double negation can not easily be cancelled, like, The speaker surely knew that China had already practiced the policy when uttering this sentence.