Your explanation makes sense.I don't think changing the address actually makes your phone arrive any earlier, it just forces caches along the logistics stack to update. I think it would have updated to the 20-22nd eventually anyway, probably at the point the next "change" happened.
Though I wanted to try and show someone from Apple that the page was not 'real time' as she said, and sadly I wasn't able to get that through to them it seems!