I think you're right that we probably discussed this on the other thread, but I can't remember the details (of even what I said :). I do not understand how you reach your conclusion from Mary's statement. Her statement was true at the time she said it, I don't think it said anything either way about the future. My version says "since I am a virgin". That is why it is understandable for her to be confused.
The perceived timing issue here is critical. If Mary thought the angel meant at some distant time in the future, then your position would be stronger. If Mary thought the angel meant "soon", then her reaction was perfectly normal. The text indicates to me that it actually was "soon".
This, like generally Protestant translations, favors Protestant theology. My original says "I know not man", a statemet akin to "I do not smoke".
There is nothing in the annunciation to suggest the event is to take place before the marriage, and common sense would dictate that the it refers to the regular offspring of the marriage.