bizarro pmax clock handling

As far as I can tell, pmax uses a standard mc146818 clock chip.

Yet, what is bizarro, is this code in inittodr (and similar in resettodr):

    /*
     * The clock lives in 1972 (leapyear!);
     * calculate seconds relative to this year.
     */
    dt.dt_year = 1972;
    dt.dt_mon = ct.mon;
    dt.dt_day = ct.day;
    dt.dt_hour = ct.hour;
    dt.dt_min = ct.min;
    dt.dt_sec = ct.sec;
    yearsecs = clock_ymdhms_to_secs(&dt) - (72 - 70) * SECYR;

    /*
     * Take the actual year from the filesystem if possible;
     * allow for 2 days of clock loss and 363 days of clock gain.
     */
    dt.dt_year = 1972; /* or MINYEAR or base/SECYR+1970 ... */
    dt.dt_mon = 1;
    dt.dt_day = 1;
    dt.dt_hour = 0;
    dt.dt_min = 0;
    dt.dt_sec = 0;
    for(;;) {
        time.tv_sec = yearsecs + clock_ymdhms_to_secs(&dt);
        if (badbase || (time.tv_sec > base - 2 * SECDAY))
            break;
        dt.dt_year++;
    }

I can only conjecture why this is here.  The mc146818 certainly can
store a year.  So why are we doing this?  Is this for compatibility with
some busted old other OS?   Ultrix?

Pray tell.  Because in all other respects this looks like an otherwise
normal mc146818 based system.  I'd much, much rather gut this weird
code, but I would like to understand why it is here.

-- 
Garrett D'Amore, Principal Software Engineer
Tadpole Computer / Computing Technologies Division,
General Dynamics C4 Systems
http://www.tadpolecomputer.com/
Phone: 951 325-2134  Fax: 951 325-2191