Think ReeVe has the sequence right... Spa was the big worry. Change had to be made before then. The improvement in load parameters allowed some teams to take more advantage because their car design could produce more load without really affecting airflow. That's why they improved.
Again, it seems as if a preseason test and a mid season test (when they return to the Euro circuits) for all teams would resolve a lot of the technical and safety problems. Locking down a tire spec for an entire season would also prove the worth of design and development and reduce the element of chance affecting results. Multiple suppliers would be better as well - but I'd be very surprised if we see multiple tire companies in F1 any time soon.
