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The EBU makes a strong recommendation that if there is doubt as to the possibility of MI you should call the TD immediately, so it is reasonable for this player to do so.
If I was the TD I would take both players away from the table separately to find out as best I could what their agreement actually is. If I believe declarer had been misinformed I would tell him so.
Whereas I am not experienced enough to dispute Bluejacks approach, I do wonder whether unless the sight of dummy makes it apparent that the explanation may be incorrect, the TD's presence at the table before the end of play creates further problems.
West would understand that South doubts his explanation even with careful removal in turn of the players, and thus would give him UI. I think that I would advise South to play to the information given, and recall me if he has been the victim of MI.
To do otherwise leaves you judging Wests play for UI.