core(5) appeared in Version 1 AT&T UNIX

Based on the scans of manual pages available at
https://www.bell-labs.com/usr/dmr/www/man51.pdf,
which are a part of the following collection:
https://www.bell-labs.com/usr/dmr/www/1stEdman.html.

Obtained from: NetBSD
Differential Revision: https://reviews.freebsd.org/D25849