@Pringlehunter: Between the original manga and its sequel it ran for 24 volumes and started in the early 80s. The cover image is probably from a later reprinting, done after considerable art evolution (since it more resembles the style of the artists works from the late 90s.)
Fun fact; The title of this page is wrong. The chapters here are from the first four books Red Fang/Akai Kiba, while Blue Sonnet is the seventh part of the series, which has no page translated chapters here.