As of 2020, "All Things" remains Gillian's Anderson's only writing credit of her entire career. It is also her only directorial credit beside her 2014 short film "The Departure."
Gillian Anderson's first draft of the screenplay was 15 pages too long and had no fourth act. Chris Carter and Frank Spotnitz stepped in to help fashion it into an X-Files episode. Indeed, one of Spotnitz's major contributions was the ambiguous opening where it is implied that Mulder and Scully have finally slept together.
One of the musical routes that Gillian Anderson and Mark Snow explored together during post-production would later evolve into the haunting "Scully's Theme". This would be used extensively throughout the eighth season.
Mulder's limited appearance in this episode is down to David Duchovny prepping his next episode as a writer-director, Hollywood A.D. (2000).