The short answer
Age it and test it. Pull every open opportunity, sort by days since the last customer initiated action, and treat anything past two normal sales cycles as dead until proven otherwise. Then apply three tests to what remains: is there a named economic buyer, is there a written next step with a date, and has the customer done something (sent a document, taken an internal meeting, looped in security or procurement) rather than just said something. Pipeline that fails two of three is not pipeline, it is a list. Do this monthly and publish the deletions, because the point is not a tidier CRM, it is that your coverage ratio stops lying to you at exactly the moment you need it to be true.