Why are there duplicates when I combine Core File years to create a database for trend analysis?

The Core Files contain all of the latest returns received by the IRS up through October/November of the subsequent year.  Thus, the Core 2009 file contains all returns received by the IRS through October or November of 2010.

We limit the file to one record per organization and take the latest return available.  If, for example, an organization with a July 1, 2007-June 30, 2008 fiscal sends its return to the IRS in early October 2008, that return is included in the Core 2007 file.  If it files later the next year -- say, in January after getting the automatic extension -- then NCCS will include the June 2008 return AGAIN in the Core 2008 file since for most research purposes, it is more important to have the organization represented in the file than not. (This return is still the most recent return available to the IRS in October or November when the IRS began creation of the new database that becomes the NCCS Core file.)

Added 07/25/2011 by tpollak, Modified 07/26/2011 by tpollak


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