As PanGalactic said, waiting to see if upgrade availability opens up near the date is a strategy that carries a risk. If there isn't any lat availability, you end up sitting in the seats you paid for - down the back.

Personally, I would never risk that as I/we have no intention of flying l/h in WT+. If we can't get upgrades to CW at the time of booking, we revise our plans and fly when it is available. The caveat here is that we are extremely flexible, not tied to school holidays and things like that, and also fly a route where [certainly mid-week] it's not hard to find CW reception availability in CW when booking >9 months ahead. Most people aren't that fortunate, of course.