In The X-Files S6 E18 "Milagro", During a scene in the graveyard, the camera pans past a headstone, which bears the names Diana and Nicholas Salinger with the year of their death as 1994. This is a reference to the late parents of the Salinger family featured in Party of Five (1994) which was also on Fox Network.
The trivia item below may give away important plot points.
Jennifer Love Hewitt made her final appearance as Sarah Reeves in Party of Five: Bye, Bye (1999) (TV Episode). The spin-off series Time of Your Life (1999) (TV Series) which is a continues on from Party of Five: Bye, Bye (1999) (TV Episode) follows Sarah as she goes to New York City to find her biological father. The series was discontinued after 18 episodes. An uncredited Scott Wolf provided the voice of Bailey Salinger in Time of Your Life: The Time Sarah Got Her Shih-Zu Together (1999) (TV Episode) which Bailey leaves Sarah a voice message on her answering message and announces that he has decided to end the relationship with her.