The entire argument rests on whether they dissasociated themselves because the change was so vastly significant to them that they could not remain a member any longer, or whether they dissasociated themselves because they never truly expected to be discovered, and picked that moment and reason to save face. It is inconceivable to me that an organization of this size and with such general competence in legal matters would be unaware that documents they had to sign each year had changed without it being pointed out to them by apostates.
If you choose to believe this and it sits well with you then hurry back to the hall. The fact that you have not yet done so, at least to me, indicates that you have not even convinced yourself of the argument you are putting forward.