引一段4.15 resolution里面的话 http://www.cgsnet.org/portals/0/pdf/CGS_Resolution.pdf
However, an acceptance given or left in force after
April 15 commits the student not to accept another
offer without first obtaining a written release from
the institution to which a commitment has been made.
Similarly, an offer by an institution after April 15
is conditional on presentation by the student of the
written release from any previously accepted offer…
简单说，4.15之后，学生也可以改变主意，但必须有release approval。
4.15之后，学校想要发
