You are answering your own questions.. :)

Little to do for us here..
But yes you are right.. it means that the right of withdrawal/right to cancel would be considered exercised when... "

Cheers

Withdrawal shall be deemed to have been effected

a valid right (say sovereignty or any other form of abstract ownership... if any other does indeed exist:)) is by definition effective in a sense that it is held (again, say, sovereignty is a "potential" – and in more senses than one – both de jure and ex consuetudine) but not necessarily exercised per actio. Therefore, to say "the right of refusal becomes effective/is made effective" is, in my view, wrong if only because it implies that at some stage it had been INeffective. The REFUSAL can be or become effective; but the RIGHT of refusal is exercised or put into effect.