It could be the similar to when stocks get paid a dividend. If company XXX on March 10th tells you they are paying a dividend to shareholders of record as of March 12th. You must have purchased your shares on March 9th to be eligible for the dividend. If you purchase the shares on March 10th you would not get the dividend because your settlement date would be the 13th.
I have no idea what would happen in WAMUQ case, but it is a great question.
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