Originally Posted by LTN Phobia

They say they do need the underlying fare class though.

Meanwhile during the run-around the upgraded class also got full so I changed the date again, but lacking in Z, and also lacking in A on the preferred flight, and BA suggested I go back to the TA to get the A (rather than Z) on the replacement date

Still ongoing. In the worst case I'll have BA process a Joker and get me the A seat on the alternative flight. I wasn't quite expecting it to get quite so complicated! I think I've spent a couple of hours talking, holding on the phone etc. Never mind.

I shall post the eventual outcome.