Complex sentence: In January 1979, this method was abolished, and certifications were instead based on unit retail sales: sales of 60,000 were awarded silver, 100,000 for gold and 300,000 for platinum.
Split into simpler sentences: In January 1979, this method was abolished, and certifications were instead based on unit retail sales. Sales of 60,000 were awarded silver, 100,000 for gold and 300,000 for platinum.