Negative past constructions such as mā faʿala and lam yafʿal both deny a past occurrence, but they can differ in the scope and perceived continuation of that denial.
In a circumstantial setting, the analyst asks how far the non-occurrence is understood to extend toward the speaker's reference point and whether that meaning is compatible with the governing event. Such nuances affect temporal comparison and the interpretation of wāw or its omission. The two negative forms should not be treated as unrestricted synonyms in every context.