According to Norton buyers guides that I have seen, there is no difference in price for Commando models. Certainly, an individual may determine that he/she wants a specific year for there own reasons but I have never seen any information that shows that a '70 is worth more than some other year. As a bike to regularly ride, some would argue against any of the drum-braked models and not care to purchase one. OTOH, someone may specifically want a drum brake BECAUSE of the look. There are folks who would not buy a Commando OTHER than a Mark III and folks who would buy any Commando Except a mark III! So it's pretty much impossible to say model year X is worth more than model year Y.