Several different people have made them. I grabbed V7 date and added

the canonical hack to have years < 70 be 20xx and built it on my Venix

box. I've not done an extensive audit, but it's the only thing I've noticed.

Warner

P.S. It's short:

commit 25485e099491fd1ae867c26043a798e47f7983ad
Author: Warner Losh <imp@freebsd.org>
Date:   Thu Nov 15 23:51:59 2018 -0700

    Apply Y2K fix to date
   
    Treat all two digit dates < 70 as 20xx and >= 70 as 19xx.

diff --git a/src/cmd/date.c b/src/cmd/date.c
index a005765..643f7e7 100644
--- a/src/cmd/date.c
+++ b/src/cmd/date.c
@@ -133,7 +133,10 @@ gtime()
        if (hour<0 || hour>23)
                return(1);
        timbuf = 0;
-       year += 1900;
+       if (year < 70)
+               year += 2000;
+       else
+               year += 1900;
        for(i=1970; i<year; i++)
                timbuf += dysize(i);
        /* Leap year */