So the Mac OS cat is old. As it happens, it is actually two years older than its 2007 appearance in MacOS X would suggest. This 2005 change, which is visible in FreeBSD’s Github mirror, was the last change made to FreeBSD’s cat before Apple pulled it into Mac OS X. So the Mac OS X cat implementation, which has not been kept in sync with FreeBSD’s cat implementation, is officially 13 years old. There’s a larger debate to be had about how much software can change before it really counts as the same software; in this case, the source file has not changed at all since 2005.