I never noticed how important exclusivity was and apparently neither did Sir Alans helper Nick Hewer because as Sir Alan said himself - if he had known he would have voided the sale - meaning Nick never mentioned it to him - if it was such a GLARING issue surely Nick would have seen it

I don't recall him being with the team that gave away the exclusivity - he may well have been with the other half of the team.
Even so, if they'd reviewed things before the results, he would have known about the exclusivity, so still could have voided it before the result was announced . As I recall the subject cropped up AFTER the winning team had left, suggesting no review had taken place at that stage. They may have checked this out between that stage and the firing stage to identify the culprit/scapegoat.
However, I'm convinced that until it gets down to four or five contestants, Sugar is pretty sure who's not going to make the grade, and he will take opportunities to
a) get the no-marks into the final 3 each week by stressing their lack of performance and "leading" the team leader to nominate in the final 3
b) aggressively target this person in the final session