There is a group forum on divorce and annulment which has a poster who is a canon lawyer. He can advise you on specific questions.
From a Catholic perspective, what matters is the conditions at the time the marriage started. So, if a Catholic marriage is entered into in ‘good faith’, that is- proper form, full consent, understanding that marriage is permanent bond etc. than it doesn’t matter what happens later. That is ‘defects’ in the marriage later don’t create a situation where it is no longer valid. However, the Church acknowledges that conditions within the marriage may occur which preclude the couple continuing to live together, even acknowledge that civil divorce may be required. But that doesn’t end the valid marriage entered into in ‘good faith’. If it is valid at the beginning it always remains so, the defect has to be there at the beginning to preclude having entered into a valid marriage.
So in reality, saying the Church annuls a marriage or grants an annulment really isn’t accurate lingustically. Since using annulment as a verb implies the church is taking an action to invalidate a marriage, which isn’t true. The Church declares a marrige to have been found null. It investigates the marriage, focusing on it’s initiation, and may issue a declaration of nullity. A declaration that was never a valid marriage from the beginning.
It is not the undoing of the marriage bond by the Church, its a statement there never was a sacramental marriage.