It's sort of interesting...in the exposition on original sin found in the fifth session of the Council of Trent
, you find statements such as: "If any one asserts, that this sin of Adam,--which in its origin is one, and being transfused into all by propogation, not by imitation, is in each one as his own...", then at the end of the section a sort of hasty out for St. Mary: "This same holy Synod doth nevertheless declare, that it is not its intention to include in this decree, where original sin is treated of, the blessed and immaculate Virgin Mary, the mother of God."
If I understand this correctly, 'propagation' is sexual reproduction. So we must wonder: If "all", even though it says "all", does not in fact include St. Mary, then what was different about Joachim and Anna's union? How far back does this exception go? Because it seems like the exception exists to ensure that Christ would be born without the 'stain' or original sin, but again, if you accept that St. Mary just didn't commit any sins, I don't see why you need to make this kind of ontological
exception for her, which seems to destroy the Catholic Church's own doctrine, as quoted above...