Splitting hairs, but you are right for at least the sound effects. The music credits are only to TR. Whether or not other members of NIN and associated personnel contributed materially to the music or not is a separate question to who got the credit, specifically. From the game manual (I still have the box, manual CD and jewel case from the original Q1 release):

Credits
SOUND EFFECTS

Trent Reznor and Nine Inch Nails

...
Music Credits

Titles of Songs or Themes (C) 1996 TVT

/Interscope Records. All Rights Reserved.

Written by Trent Reznor (C) 1996 Leaving H

ope/TVT Music. ASCAP All Rights Reserved.