Complex sentence: As one of the most iconic typefaces of the twentieth century, derivative designs based on Helvetica were rapidly developed, taking advantage of the lack of copyright protection in the phototypesetting font market of the 1960s and 70s onwards.
Split into simpler sentences: As one of the most iconic typefaces of the twentieth century, derivative designs based on Helvetica were rapidly developed. This profusion of pirate copies took advantage of the lack of copyright protection in the phototypesetting font market of the 1960s and 70s onwards.