I'm GGL now and have been flying with BA extensively in last 3 years and never saw an OP-UP. Closest call was GVA-LHR where they upgraded a crazy number of people (I think I saw 9 Borading passes on the counter). when I asked what the criteria was they told me it was the price of ticket (i.e. the more expensive got the upgrade) - I think this is unique to Geneva though.