RRD Graph question - dynamic fields

Hi I am using xymon/rrd to graph the number of events / subevents persisted to a database on a daily basis.  This is to gather trending and also for monitoring.  I am trying to graph the number of 'subevents'.The problem I am facing is that not all subevents show up each day and therefore I receive this error,...is there a way I can get the rrd to ignore the definition if it is not present in the rrd file or do i have to stub each subevent to '0' until an event occurs for it ?"No DS called 'REQUEST AUTHORIZED' in 'ACCESS_EVENTS.rrd'"
Thank you for any guidance here.
SJC