The additional call might have been offered in the previous half hour and might have been completed in the current half hour. Thus, there will always be a difference in the offered and answered calls.
In the attachment, the previous half hour period had 6 offered, however only 5 answered. The 6th call got completed in the duration from 10AM to 10.30AM, hence shown as completed task in the 10AM half hour report.
You can verify and confirm this by using database query on the t_Termination_Call_Detail. Check for the number of calls offered from 9.30 to 10AM and check the start time and end time of the calls, you will get a clear picture.
