Yes, as I tried to explain in my OP. Whilst there is full availability on W class on LHR-US gateway and US gateway-GRU, if you combine them into LHR-GRU, it all disappears. The 1K desk is seeing the same thing. So it's a matter of either taking the weird CO codeshare or just forgetting about upgrading and slugging it out in Y on a more direct route (or indeed booking LH in V class, but that's more expensive than PE on BA so a bit hard to justify).