It might be known to other expert flyers here, but to me it was a discovery that the Skymiles price of an award ticket can go down after booking

Yes, it is a ridiculously short and cheap flight (LAS- LAX), but with this learning it is useful to check your more expensive ones.

I bought the original ticket 3 weeks before the flight for 5900 Skymiles, and a week later I re-booked it at 4600 miles, cancelling the first booking. Surprisingly, the buy-up to first class offer costs the same. Finally, the dollar price they ask for the flight hasn't changed.
Discovered this accidentally looking for different options.