[Zelandakh]

I think the UI issue is a bit of a red herring here, so let's instead consider the more general case where you are in this position without having received UI (behind screens, online, etc). With my last partner, we actually had an agreement for situations like this while she was learning the system. When she could not remember the system any more, she would simply jump to the most likely contract. This was pretty much always something impossible and therefore acted as an immediate indicator that there was a problem.

To hautbois, I guess you have not played many relay systems. The problem is that your subsequent bids may not refer to the same cards after the misbid as before. For example, say you showed 2 kings and denied a king where you have one. When you show the other king, partner only know about this one and expect to find out where you hold a second king. But you cannot go back to show it, so you simply have to lie.