How would the balancers know what year chassis they were mounted to?
Just kidding.
I would use them regardless of what year I'd be owning. After having a set myself I would never be without them again.
I bet many others who use them feel the same way.
It doesn't improve the ride on a bus with proper tires but it does eliminate the ocasional tire imbalance on new tires, ocasional thrown wheel weight, reballancing at half life and all those related costs.
Get them.
Tire balancing is only as good as the installer and the machine.