counter reading was not picked in the billing program

Hi Experts,

I need clarification on one question related to billing in service contracts.

I have 2 contracts.But I could see differences in billings.
So this has been replicated in one sample scenario as below.

1. T-754827 (T GROUP)
2. F-754823 (F GROUP)

Counter readings of T-754827

Value Time Stamp-->Counter reading-->Date on reading entered (creation_date)

30-OCT-2012 00:00:00-->100-->18-FEB-2013 4:34 PM
31-OCT-2012 00:00:00-->150-->19-FEB-2013 9:53 AM
30-NOV-2012 00:00:00-->200-->19-FEB-2013 9:53 AM

Billing program run times:

19-FEB-2013 9:20 AM end time
for 1-Oct-2012 to 31-Oct-2012-->100-0=100 (net reading)

19-FEB-2013 9:55 AM end time
for 1-Nov-2012 to 30-NOv-2012--> 200-100=100 (net reading)

Counter readings of F-754823