Intuitively, I would expect the current list of “Top Locations” to remain in place and in the same order, but simply with an additional bar showing last week’s values.
In the case of no data for the previous week, as in your description of Australia, add an empty bar to be explicit about the “emptiness” of last week’s data, and maybe a short bit of info describing the data, or, if you feel it flows better, as a footnote.
(Still do keep the data on the right; I just didn’t mock it up. Perhaps Australia’s percentage change label is where the asterisk belongs to indicate that this data has an explanation.)
Also relevant, I would recommend considering using flat ends for your bars, specifically when comparisons are necessary. The rounded ends are more difficult to see how visually significant the difference in length is.