Usage Anaylsis by date range - same range showing different results

We have a usage analysis that runs by date range such as 03/01/2015 - 03/31/2015. The user selects the dates. Fields are # of records created, # of records deleted, # of records updated, andd # of total logins. User just reran analysis for some previous months, and reports that they are getting different data for same date range previously ran, such as 03/01/2015 - 03/31/2015. The # or records created and # of records updated are now bigger than previously shown for the same month. Is there something that needs to be changed in order to return the same results for same previous month ranges selected?