I saw your question and that you are waiting for a long answer.
I am a partner of Sonoff and I will be happy to answer you:
I did some tests:
- The new version supports the training of 4 buttons on one gang.
- They can also be from different remotes.
- Each subsequent training - 5, 6 .. button overwrites the first, second button, and so on until you overwrite all 4.
- The interesting thing is that you can learn the given button / remote on several gangs - ie. on one remote control to start/stop 2, 3, or all 4 gangs with only one button on the remote controller.