You, errrrr, you seem to be tying yourself in bigger and bigger knots here, Sabby. Let me try to break down what I see as the flaw in your argument.
Original Sin is a concept within the Catholic church. The Pope infallibly decreed that Mary didn't have it. Original sin has no objective existence, it is entirely contained by the church. So who has it and who doesn't is entirely a matter for the Church. As Louise says, it had long been (orthodoxly) held that Mary was free from Original Sin, but it wasn't confirmed until the 19th century. From that point on, it was anathema to believe otherwise. You might, I do, that's fine. Neither of us are Catholic.
However, for Catholics the matter of faith is now settled. She was without Original Sin. As such, she ascended directly to heaven. This all follows by definition. There is literally nothing controversial there, if you find something so then I suggest its because there's an aspect you haven't understood.
You seem to be claiming by "Mary existed, at X time, and ascended to Heaven is NOT a claim you can make with no possibility of error" that this is a discussion open to, I dunno, eyewitness accounts and checking the guestbook at the pearly gates. Its not, for the simple reason that there is no proof of the existence of heaven. Heaven, everything about it and who goes there and doesn't is a matter of faith. Which the Pope is, in certain circumstances, infallible on.