485 approval notice (hard copy)received

6/25 收到email -- approval notice mailed on 6/23
今天(6/29) 收到寄來的approval notice.
No LUD after 6/25, no "card order" or "welcome notice" from email.
有遇到類似情況的嗎？請問大概什麽時候能收到卡？
為什麽看到大家都是在幾天內陸續收到幾個不同的email,然後馬上收到綠卡？