In October last year I was flying to DXB in FIRST. Sheena was was on a CW BA Miles ticket. We used OLCI and at the Fast Bag drop at EDI the check-in agent made some notes in Sheena's booking that I was in F. The flight had being showing full for weeks and the check-in agent confirmed it was oversold. Just before departure Sheena went to the desk in Concorde Room and came back with a new BP and a big smile!

In December when flying WT+ EDI-LHR-JFK I used OLCI exactly 24 hours before my EDI-LHR leg. I was delighted (and very surprised) to see we had already been upgraded to J. Again the flight had shown as sold out in WT for many weeks.

I think it boils down to the fact that if you are going to be upgraded, you will be upgraded regardless of what mechanism you use to check-in.