Each of the UCs have the ability to know what the others are doing with regard to admissions. The common UC app accumulated at a centralized site is sent to each university as only demarcated by a check mark by the campus(es) to which the student wishes it is sent.
Therefore, there has to be an honor system by each of the UCs not to peek at what colleges some of these students have applied and subsequently been admitted, but I don’t know if that would be reasonable to expect this. I think that social media can also be a conduit to which colleges spy on others with regard to specific students who have been admitted. UCLA and other colleges admittees are certainly out there as seen on Facebook, Instagram, etc. I think therefore that taking off of W/Ls nearer to the commitment deadline is here to stay, and colleges will be trying to steal away committed students from each other.