Just as an update, we got to the airport fairly early and had been allocated: 1G, 2D, 3E and 3G - which was actually much better than I had seen available on the seatmap in the time approaching the flight.

The person in 2H kindly agreed to move forward and swap with our 1G, and he actually had 1E empty for most of the flight, except for a pilot for a couple of hours.

So, I can only assume we never really were on standby, but for some reason IB didn't want to allocate seats when we did OLCI.