I have less of a comment than a non-scientific observation.

This was mentioned way upthread (I think by the Cow), but my cunning plan of using general Y alerts as a proxy for Lat Y is no longer that clever.

I've seen more and more flights where Lat and (whatever lowest available) Y point 'prices' are diverging. And using J as a proxy doesn't seem to work much better either. Not to fault the Cowtool at all, Google Flights doesn't support branded fares well at all for tracking revenue flights.

It's possibly just a coincidence that I'm noticing this more now, and it's likely just the flip side of when I've seen Lat fares higher than J and other anomalies. Either that, or Lat fares are just extra-dynamic. Not something that we can reverse engineer I guess.