UC supplement/augmented review?

<p>I heard that the UCs sometimes give out supplements to certain applicants late Jan or early Feb. Just wondering, what are these supplements given out for and how often do people get them? Some have said these supplements are given to borderline applicants, so adcoms can see 1st semester senior grades and new awards/accomplishments. Since I have a high SAT score and below average GPA with an upward trend (also an essay that emphasizes my improvement), is it likely that I'll be given a supplement and be asked to send my 1st semester senior grades? Sorry if these were stupid questions</p>