Hi,
Standard data source pulls the data which were entered into SAP by standard SAP procedure.
Seems like end users may entered the materials(which are not coming while pulling at RSA3 or full load) in abnormal way or they might be entered directly into table.
So note down the materials which are not coming into bw, seek MM team help and find the cause.
Or those might be something differ with other materials.
So you need to find the cause at source side only. MM team can find that cause.
Thanks