An affirmative past reports an occurrence with a specific event-time. A negative past denies an event and does not inherently identify an equally specific positive occurrence. Its scope may therefore be interpreted over a broader interval that remains relevant at the reference point.
Compare جَاءَ زَيْدٌ وَقَدْ رَكِبَ, where an earlier or accomplished riding event is asserted, with جَاءَ زَيْدٌ وَمَا رَكِبَ, where riding is denied. Their circumstantial interpretation depends on different temporal relations, so a single mechanical explanation of wāw is insufficient.