You know you can simplify the IF/Then test blocks (actually eliminate them) and just use 2 statements.

SDC_Block = (Current_Event * 4) - (3 - (Event_Record_IDX / 256))
SDC_PAGE = Event_Record_IDX - ((Event_Record_IDX / 256) * 256)


This will save you >100 code words or 194 bytes of code space.