In the BSD /COPYRIGHT, it's not deleted, but rather this addendum appears (truncated for brevity...)
NOTE: The copyright of UC Berkeley's Berkeley Software Distribution ("BSD")
source has been updated. The copyright addendum may be found at
[url]ftp://ftp.cs.berkeley.edu/pub/4bsd/README.Impt.License.Change[/url] and is
included below.
July 22, 1999
To All Licensees, Distributors of Any Version of BSD:
As you know, certain of the Berkeley Software Distribution ("BSD") source
code files require that further distributions of products containing all or
portions of the software, acknowledge within their advertising materials
that such products contain software developed by UC Berkeley and its
contributors.
<snip>
Effective immediately, licensees and distributors are no longer required to....
And yeah, it does say "deleted in its entirety". However, many of the files in ~/src still carry that paragraph, 4 years later...hmm, maybe I should submit patches 😃
Well, I'm sure if anyone told us, they'd have to kill us, or at least chop off some body part unless we signed a non-disc in our own blood, but there is this, which I'm sure would be very interesting to me if I knew more about the history and design of software ....