about the same time they release them for SWU

With the change in premium seating and reducing capacity
With the changing economy situation effecting/enabling paid premium travel
With the merge in progress
....

Suspect there is probably little value in in historical data, even the 330 day window is not reliable from some reports.

Not a terrible helpful response but this appears to be the new reality - confirmed upgrades at bookings are just plan harder to do (but they do still occur).