Hope you can help. I have a multi sector booking which includes BA (x 2) and AA (x 2). This will be issued on BA stock through a travel agent. Reading the forum and Avios guide - if I'm reading correctly - it says I won't be able to upgrade the BA legs if availability comes up.

I had a very similar booking last year through the same travel agent and I was able to upgrade the return leg BOS to LHR into First. Was I lucky, misreading the rules or have the rules changed? Thx