Resolution:
The upper bound for the DateTime data type corresponds
to the upper bound for the standard C language time_t data type.
The InConcert Programmer's Reference Guide (p.7-3) description of
CIcDateTime_convertToTimeT describes the time_t data type as follows:

------
    The time_t data type is defined in /usr/local/include/sys/stdtypes.h
    and is as follows:

    typedef long time_t;
    /* value = secs since epoch */
------

The maximum value for this is 2^31 - 1 or 2147483647 seconds,
corresponding to slightly more than 68 years, or from
1970 to 2038.