Complex sentence: Through the 1950s opening-roof convertible automobiles were sometimes called drop-head coupés, but since the 1960s the term "coupé" has generally been applied exclusively to fixed-head models.
Split into simpler sentences: Through the 1950s, opening-roof convertible automobiles were sometimes called drop-head coupés. Since the 1960s, the term "coupé" has generally been applied exclusively to fixed-head models.