@harrypotter112, that UC Irvine website page you mentioned is from 2006 and relates to those who were applying for entry into fall 2007. It is from a time when UCs actually required subject tests and it is no longer in effect. The current all scores rule is inapplicable to subject tests.
@Aneem00, I was referring to the SAT. There has not been one report in the last decade of any student being rejected or disadvantaged in the admission process in any way at the UCs for failure to provide all scoress of any tests, SAT, ACT or subject tests.
As to UCs knowing whether you used score choice, at the time of detetmining admission it is not likely since College Board does not tell colleges you have withheld any tests when you order them sent. The UCs may receive information that shows you withheld scores after you are admitted. The UCs do not require your high school transcript until after you are admitted and finish high school. You self-report courses and grades when you apply. There are high schools that put all your scores on the official transcript sent to colleges and thus the UCs could learn you withheld a score if your high school provides all scores on the transcript sent after you graduate from high school. Despite that possibility, there have been no reports of any UC applicant having an admission decision rescinded for failure to provide all scores.