Back back in the day, BSD was poised to take over the world.
But unexpectedly they smacked the bear on the nose and wound up in a year's long lawsuit which put the future of BSD in peril.
In the end, everything was resolved with USL asking the CSRG (those responsible for BSD) to create a redacted release. This release was missing a few files and could not be compiled into a working release.
The open source projects (NetBSD, FreeBSD) scrambled to replace the missing parts and eventually released legally clean and unencumbered versions of their BSD-based operating systems.
Several years later, "historic unix" was released openly by Caldera (before they became the SCO group?), which put the formerly contested files out into the open.
A couple of years later, in 2004, a list of the contested files was released by Groklaw.
Here is the list, as far as I'm able to piece together:
Six Missing Header Files:
sys/sys/buf.h
sys/sys/proc.h
sys/sys/shm.h
sys/sys/tt y.h
sys/ufs/dinode.h
sys/ufs/inode.h
“Restricted Files” (26 files):
sys/kern/init_main.c
sys/kern/kern_clock.c
sys/kern/kern_exec.c
sys/kern/kern_exit.c
sys/kern/kern_physio.c
sys/kern/kern_sig.c
sys/kern/kern_synch.c
sys/kern/subr_rmap.c
sys/kern/sys_generic.c
sys/kern/sys_process.c
sys/kern/sysv_shm.c
sys/kern/tty.c
sys/kern/tty_subr.c
sys/kern/vfs_bio.c
sys/kern/vfs_syscalls.c
sys/sys/buf.h
sys/sys/proc.h
sys/sys/shm.h
sys/sys/tty.h
sys/ufs/dinode.h
sys/ufs/inode.h
sys/ufs/ufs_bmap.c
sys/ufs/ufs_disksubr.c
sys/ufs/ufs_inode.c
sys/ufs/ufs_vnops.c
usr.bin/cpio/cpio.c
