I flew last week LHR-YYZ arriving at 10:30PM and left the next day at 8PM YYZ-SYD. They pulled the SSW in LHR and noted it in the file. I had no problem in YYZ since the connection was less than 24hrs and the notation in the file was enough for them to upgrade me on the second portion. Thank goodness there was space available.
It is interesting to note that because I booked YYZ-SYD, if there was space available on the first leg to YVR but not on the YVR-SYD they apparently could not upgrade me on this segment alone. I was told that the staff in YVR could upgrade me for the second leg if there was space available. I think I would book each segment separately next time if the price was the same.