How compatible are newer Reply models with older ones?

If we look at Fleetwood made Reply systems then each type of keypad requires its own base station. Some Reply softwares allow multiple types of Reply keypad systems to be used at the same time thus allowing you to use all your keyapds. Some Reply voting softwares allowing mixing of all the Reply models, others don't. The Reply Worldwide and the now discontinued Standard keypad are totally compatible on Reply softwares as long as each type of keypad has its own base station.