Sorry I can't help. But I appreciate your problem as I read and read and re-read the new BAEC T&C after the AA/IB join-up and couldn't work out what they mean.
I don't think the NCE, FCO end is an issue they are both Europe 1 as far as I know.
Hopefully someone can point out why you can't upgrade from I to F given the other legs are in valid upgradeable codes (Y & J). Are you sure the SGF legs aren't in something like M or V for some reason?

In such a possible situation I will (these days!) call and try the booking over the 'phone, and if I'm told I can't upgrade then I'd ask why. If I'm not convinced I ask them for an alternative that will work, or another agent if I'm uneasy about the agent's knowledge.