请问什么叫托福写作分数无效

申请2020fall，马上就4.15了有些学校还没消息，就写了一份邮件催了催。结果Purdue这么回复我
“I am writing to inform you that we tried to recommend your application for admission to our program, but our Graduate School pointed out that your TOEFL writing scores are no longer valid. Do you have updated TOEFL scores by chance?”
我的托福是2018年2月4号考的，所以要求托福入学时有效的学校都没申请。
但是Purdue应该没有这规定，网申界面上也都显示托福成绩received。
请问大家有没有什么办法argue一下。