score:6
I checked in the contemporary British press for 1955 (sadly I do not have access to that for other countries). I could find a couple of different photographs - probably taken about the same time as your second one, they're on the same balcony, but subtly different in terms of the angles and so on. I guess different agency photographers at different moments.
The caption of the one in the Illustrated London News is interesting (my emphasis):
After the signing, [the ministers] came out on a balcony of the Palace and were greeted with great enthusiasm. Cheering continued for over an hour, and the foreign ministers and Herr Raab, the Austrian chancellor, were repeatedly called out, both singly and together, while flags, handkerchiefs, and hats were waved.
So it seems quite possible that the photos were taken at different points over a period of time, rather than them coming out in one place and immediately going to come out at another. This doesn't explain why they specifically went to different balconies, but it makes it seem a bit less odd.