Hi Yang,
Labels and
LabelIds are manually implemented in your objects upon creation or through modification using the mutate() method. If this step was not taken, then that would be the reason as to why the report fields in question do not have values returned.
That said, could you confirm if someone from your team has indeed added labels to all your keywords and are now facing the discrepancy as you described? If yes, could you provide to me your clientCustomerId and the complete
report definition you used when you generated the report?
You may reply to me via the Reply privately to author option.
Thanks and regards,
Peter
AdWords API Team