Calendars apply to the subsequent date production, not to the entire DateValue. Hence,
DATE FROM 1670 TO 1800 means DATE FROM GREGORIAN 1670 TO GREGORIAN 1800DATE FROM 1670 TO JULIAN 1800 means DATE FROM GREGORIAN 1670 TO JULIAN 1800DATE FROM JULIAN 1670 TO 1800 means DATE FROM JULIAN 1670 TO GREGORIAN 1800Because some systems may show dates as-is to users and because not all users understand the above rule, it is recommended that calendar tags be included if any date is non-GREGORIAN. It is recommended that the calendar tag be omitted if all dates in a payload are in the Gregorian calendar. Hence, the recommended forms of the previous 3 dates are
DATE FROM 1670 TO 1800DATE FROM GREGORIAN 1670 TO JULIAN 1800DATE FROM JULIAN 1670 TO GREGORIAN 1800