The gemarra often employs the different types of derashos/hermeneutics such as kal vachomer/a fortiori arguments and hekesh/juxtaposition of phrases or terms. Also often, is these derashos are rejected due to some flaw, known as a pircha. For example, a law can't be derived from one verse to another through a hekesh because there's some special reason the first verse should have the law, which doesn't apply to the second verse.
Rabbi Yosef Tzvi Salant in Be'er Yosef suggests that when a pircha is introduced, the derasha isn't totally rejected. It remains a doubt, and in fact it could still prove true, if some later evidence appears that it's true.
I was wondering if this is his own insight, or is there an earlier source for such an idea, or is this not even a novelty, but the basic understanding of derashos/pirchos.