Delta records with 0CO_OM_OPA_6

I have a question regarding how the deltas work for  the datasource 0CO_OM_OPA_6.   We are loading directly to the 0opa_c11 cube.  It seems that we are missing some delta records but not all of them for a particular day.  I looked at the function module and it has a delta mode and a full mode.     It looks like it reads this table, BWOM2_TIMEST, to get the time stamps.  How can we lose some records?