Complex sentence: Whether or not such structures were inspected is unknown; it seems not, as several more collapses occurred some years later, at the Inverythan crash and the Norwood Junction rail accident in 1891.
Split into simpler sentences: Whether or not such structures were inspected is unknown. Later events seem to negate the possibility, because several more collapses occurred some years later, at the Inverythan crash and the Norwood Junction rail accident in 1891.