Another Y->J (going from Eco Light K to P) datapoint:

LH459 SFO-MUC (06.05.2024) Bid Upgrade 710EUR (I think 670EUR was minimum). Direct upgrade price was more than 2k EUR 2-3 months before the flight, fluctuated around ~900-1100 2-3 weeks before the flight, plenty of seats still open.
Bid accepted 72h prior to departure.