In C:\SmarterMail\Domains\<domain>\Users\<user>\XXXXXXX_calendarData.xml.
If you copy from the first

<Event>

to the last
</Event>

In each file and stick them in one single file in between

<CalendarData ID="xxxx"> and </CalendarData>

AE1279A3_calendarData.xml is usually the main primary calendar for user's so you'll want to combine them into this file.
If you do this while your service is turned off, when you turn it back on it should load them all under the same calendar. If you need more help with me explaining it I can.