"Most interesting were the remotes for our minisplits, which tranmit the whole state for the minisplit"

I think this is necessary because A/C remotes often have a screen showing the state. If you transmit the whole state then, as long as the most recent button press made the unit beep, you can be sure that the state on the remote screen is correct. If you were to transmit deltas only (e.g. temperature up/down) you could eat out of sync and have no easy way to get back in sync.

True! Used to have an A/C unit with this problem. Covering the IR emitter with a finger would desync the remote's state and that of the actual unit. Temperature was the easiest to sync back: just keep lowering it until both systems reach the temperature floor.

This problem still shows up today in limited forms. I have several A/C units of the same model and the same remote. Sometimes the remotes get mixed up and I end up trying to use a remote in the A/C off state to control an A/C that's on, and it does nothing until I cover the IR emitter and "turn it on" first.