Complex sentence: However, he did not number his symphonies until 1956 when "Symphony in D minor" appeared, and his publisher, concerned that the work might be confused with his "Symphony in D" of 1943, suggested the new work should be called number 8.
Split into simpler sentences: However, he did not number his symphonies until 1956 when his "Symphony in D minor" appeared. His publisher, concerned that the work might be confused with RVW's "Symphony in D" of 1943, suggested the new work should be called number 8.