GL account is empty for some co document nos

Hi Experts,

i am sap bi resource and in bw we got some controlling records whose GL account is empty.

i checked in bseg table the corresponding reference doc nos and there i could see the gl account having some value.

But when i check the covp table gl account is empty for these co documents.

In bw we use one datasource 0CO_OM_CCA_9 which is based on table covp.

please let me know what could be the possible reason for this.

Thanks.