Complex sentence: Congress authorized an explosion of commemorative coins in 1936; no fewer than 15 were issued for the first time, plus several from prior years, senior among them the Oregon Trail Memorial half dollar, first struck in 1926.
Split into simpler sentences: Congress authorized an explosion of commemorative coins in 1936; no fewer than 15 were issued for the first time. Several coins minted in prior years were produced again in 1936, senior among them the Oregon Trail Memorial half dollar, first struck in 1926.