Yes, thanks for this extra comprehensive detail.

There are a few carriers with fares lower down the scale which do qualify, but I think these are typically intra-Europe where redemptions are usually poor value anyway.

SQ is the real kicker, where it's impossible to upgrade from Y to J on routes with Premium Economy (i.e. the ones from Europe). You can't, under the scheme, upgrade from Y to Y+, nor even redeem directly into Y+.