CO09 does not show the confirmed sales orders

Hi,

Normally, when I go to transaction CO09 it shows me the sales orders / positions as wel as the deliveries lines that were confirmed for a material.

In some cases it just shows me the deliveries positions and the sales orders numbers are not shown, so I can not identify from which sales order the cinfirmation was done.

When does this cases happen? Is there something I can do, so that it always shows me the sales order numbers?

Thanks a lot!